Xdoctest

Fixed
* Minor issues with release tarballs.

Fixed
* Color issues on win32


Changed
* Moved to CircleCI deploy scripts

Fixed
* Bug where references to doctest variables were never released

Added
* Documentation improvements
* Minor text fixes

Added
* `pip install xdoctest` can now specify `[colors]` or `[jupyter]`
* Enhanced REQUIRES directive behavior, multiple comma-separated requirements
can now be listed in one directive.
* Xdoctest can now be run inside of Jupyter notebooks / IPython sessions
* Xdoctest can now be run on Jupyter notebooks (Note that in general it is
better practice to write a module)

Fixed
* Bug in `doctest_callable` where it would not populate globals from the function context.

Changed
* Renamed `Config` to `DoctestConfig`
* Renamed `static_analysis.parse_calldefs` to `static_analysis.parse_static_calldefs`.
A temporary function with the old name is exposed for backwards compatibility.
* Changed argument name from `modpath_or_name` to `module_identifier` in several functions.
This is to better indicate its coercible nature as either a module path, a
module name. This change impacts `doctest_module`, `parse_doctestables`,
`package_calldefs`.

Added
* The REQUIRES directive can now inspect existence or values of environment variables.
* Added top-level `doctest_callable` function, which executes the doctests of a
function or class.
* Support for `NO_COLOR` environment variable.

Fixed
* `IPython.embed` and `ipdb.launch_ipdb_on_exception` now correctly work from
inside doctests.
* Small incompatibility with `pytest-matrix`. See 82