Steno3d

Major Features
- `Vector` - new `CompositeResource` that uses `Mesh0D` and defines `vectors` at each point. This allows uploading of vector fields to steno3d.com.
- Currently, this only supports vector direction and not vector magnitude.
- OMF support - `Project` now has a class method `from_omf` which constructs a Steno3D project from an OMF file or `Project` created in the OMF API

Minor Changes
- `Mesh3DGrid` now supports geometries that are rotated and/or non-axis-aligned
- This is done by defining vector directions for each axis `U`, `V`, `W` (corresponding to `h1`, `h2`, `h3` respectively)

Minor Changes
- New `steno3d.examples` modules `Brain`, `Rocket`, and `Tsyganenko`
- Updates to `Airports` and `Topography`

Bug Fixes
- Fixed a bug where bad web response gave a `JSONDecodeError` rather than a useful error.

Minor Changes
- Allow `Comms` methods to be properly overrriden
- Necessary for steno3d upload integration test
- Return `dict` in `Comms` methods rather than `requests` object

Minor Changes
- Project query now obtains resource JSON from a separate request rather than the expanded project JSON. This will ensure compatibility when the project JSON is reduced.
- Mesh grid tensors (ie `h1`/`h2`/`h3` may now be integers). This simplifies the creation of regularly spaced grids and building from JSON.

Bug Fixes
- Fix URL string formatting
- Fix Mesh2DGrid Z array download

Bug Fixes
- This update eliminates incorrect deprecation warnings were showing up in Python 2 because of `newsuper`.

Minor Features
- Mesh2DGrid:
- `x0` has been deprecated in favor of `O` to match naming convention
- `U` and `V` are now traits of this mesh in order to support non-horizontal meshes
- Parser:
- `Project` is now a trait of the `BaseParser` class. This aids validation and further simplifies writing new parsers
- Examples:
- New .obj file example to support parser notebook
- Testing:
- Test the open-source parsers on build and tests against pre-release of `traitlets`

Bug Fixes
- Fix bug using `observe()` with new `traitlets 4.3`
- Remove `logout()` `atexit` register; this is currently logging the user out of all steno3d.com sessions, not just the single upload session