Weasyprint

WeasyPrint now depends on html5lib-0.999999999.

Bux fixes:
- Fix Acid2
- [325](https://github.com/Kozea/WeasyPrint/issues/325):
Cutting lines is broken in page margin boxes.
- [334](https://github.com/Kozea/WeasyPrint/issues/334):
Newest html5lib 0.999999999 breaks rendering.

Bug fixes:
- 263: Don't crash with floats with percents in positions.
- 323: Fix CairoSVG 2.0 pre-release dependency in Python 2.x.

Bug fixes:
- 189: `white-space: nowrap` still wraps on hyphens
- 305: Fix crashes on some tables
- Don't crash when transform matrix isn't invertible
- Don't crash when rendering ratio-only SVG images
- Fix margins and borders on some tables

New features:
- [295](https://github.com/Kozea/WeasyPrint/pull/295):
Support the 'rem' unit.
- [299](https://github.com/Kozea/WeasyPrint/pull/299):
Enhance the support of SVG images.

Bug fixes:
- [307](https://github.com/Kozea/WeasyPrint/issues/307):
Fix the layout of cells larger than their tables.

Documentation:
- The website is now on GitHub Pages, the documentation is on Read the Docs.
- [297](https://github.com/Kozea/WeasyPrint/issues/297):
Rewrite the CSS chapter of the documentation.

New features:
- Support the `empty-cells` attribute.
- Respect table, column and cell widths.

Bug fixes:
- [172](https://github.com/Kozea/WeasyPrint/issues/172):
Unable to set table column width on tables td's.
- [151](https://github.com/Kozea/WeasyPrint/issues/151):
Table background colour bleeds beyond table cell boundaries.
- [260](https://github.com/Kozea/WeasyPrint/issues/260):
TypeError: unsupported operand type(s) for +: 'float' and 'str'.
- [288](https://github.com/Kozea/WeasyPrint/issues/288):
Unwanted line-breaks in bold text.
- [286](https://github.com/Kozea/WeasyPrint/issues/286):
AttributeError: 'Namespace' object has no attribute 'attachments'.