Toyplot

This version corrects a problem with the documentation generated at https://toyplot.readthedocs.io, there are no code changes w.r.t Toyplot 0.17.0.

* Moved sample datasets into the `toyplot.data` module.
* toyplot.mp4.render() generates H.264 output.
* Restored `toyplot.canvas.AnimationFrame.set_datum_text()`, which was with the debut of rich text..
* Use the Python warnings module for deprecation warnings.
* Disabled pylint testing on Travis-CI, it was too much of a moving target.
* Simplified the animation API.
* Switched to Python 3 as the primary build and test environment.
* Removed obsolete dependencies from the Travis build.
* Disabled PNG downscaling for ghostscript versions < 9.14.
* Table cell data can be rotated.
* Moved image manipulation into a new `toyplot.bitmap` module.
* Added a bitdepth option to `toyplot.bitmap.to_png()`.
* Allow default canvas width and height to be set in `toyplot.config`.
* Fixed a false-positive comparing XML documents.
* Explicit colormap domains aren't required for toyplot.canvas.matrix().

* The -toyplot-anchor-shift property didn't affect text layout extents correctly - thanks to Deren Eaton.
* Corrected a broken link in the documentation - thanks to Github user kannes.
* Removed the dependency on colormath, which is currently broken by an API change in networkx.
* Replaced toyplot.compatibility with six, since the latter is already a transitive dependency.
* Replaced toyplot.color.near_black with toyplot.color.black
* A hyperlink can be set for an entire canvas.
* A hyperlink can be set for a set of Cartesian axes.
* Per-datum hyperlinks can be set for scatterplots.
* Moved documentation- and test-specific code out of the main library.
* Set a reasonable stroke width when drawing text layout boxes for troubleshooting.
* Clarified in the documentation how tick locators can affect the visible domain.
* Corrected copy-n-paste errors in many docstrings.
* Fixed many broken documentation crosslinks.
* Supplied many missing docstrings.
* Removed the WebM rendering backend, which has been broken and unused for a long time.

* Markers can be embedded in any text, including tick marks, legends, labels, and table contents.
* Hyperlinks can be embedded in any text using the &lt;a href="..."&gt; tag.
* Legends are implemented using table coordinates, so legends can be customized using any table feature.
* Started a new documentation section for case-studies, with graph community and neural network examples.
* Started a new section in the documentation for projects using Toyplot.
* Callers can define their own custom marks, and modify rendering for existing marks, using the new rendering API.
* Defined a new API for embedding Javascript in HTML markup, for use with custom marks.
* Graph visualizations can export vertex and edge data as CSV tables.
* Added support for head, middle, and tail markers on graph edges.
* Added an `offset` property for Cartesian axis labels.
* Toyplot colors are allowed as style property values.
* Per-series and per-datum colors can be specified using Python sequences as well as numpy arrays.
* Error messages specify which CSS properties are allowed.
* Deprecated the `gutter` parameter in favor of `margin`, which can specify separate left / right / top / bottom margins, if desired.
* Added `toyplot.html.tostring()` to simplify generating HTML.
* Added a style option to `toyplot.html.render()` and `toyplot.html.tostring()`.
* Added a `palette` argument to override the default series palette when creating axes.
* Text markup didn't include units for font-size, causing incorrect results on Firefox.

* Completely new text layout that explicitly positions all text.
* Experimental support for hyperlinks in table cells.
* Return a scalar instead of an array when accessing toyplot.data.Table using a single column name and row index.
* Correct a bug that caused text baselines to be computed incorrectly in PDF output.
* Add pylint to the regression test suite.
* Allow font-family to be used in inline rich text styles.
* Created an API to retrieve font metrics.
* Disable obnoxious colormath logging by default.
* Mention XML escaping for rich text in the user guide.
* The "<" and ">" markers were rendered reversed.
* Eliminate warnings using a Pandas series as the baseline for a bar plot.
* Make it easier to disable graph vertex labels.
* Allow stroke-linecap for CSS line styles.
* Improve rasterized PNG output quality.
* Warn when using older versions of ghostscript that produce lower-quality PNG output.
* Suppress the "No handlers could be found for logger toyplot" warning.
* Rewrote the logic for detecting Ghostscript.

- Allow fill marks to be used as annotation.
- Explicitly disable data export from annotation marks.
- Add an experimental `<axis>.domain.show` parameter to control whether the domain is displayed using axis spines.
- `toyplot.data.read_csv(convert=True)` will try to parse integer as well as floating-point types.
- Completely rewrote the table coordinates implementation.
- Table coordinates support advanced, numpy-style indexing for all rows, columns, cells, gridlines, and gaps.
- Added API to delete table coordinate rows and columns.
- Added API to insert table coordinate rows and columns.
- By default, all table cells are vertically and horizontally centered with a default font.
- Matrix visualizations no longer bold row and column indices by default.
- End-users can export CSV data from table coordinates and matrix visualizations.
- Added table-cell bar plots and line plots that use the data already contained in the table.