Per http://docs.travis-ci.com/user/migrating-from-legacy

Lazy loading of pure Python tokenizer

Use 3.5 nightly in build matrix

'nightly' now follows Python 3.6
Use '3.5-dev' for Python 3.5 nightly
http://docs.travis-ci.com/user/languages/python/#On-demand-installations

Partially resolves issue #112

* Remove unnecessary win_install.ps1.
* Add appveyor version update to release script.
* Make setup.py's pure Python fallback code less intrusive.

Issue #26 Use pure python on compilation failure

'setup.py test' also uses SystemExit, with args[0] as False.
Detect and re-raise.

Add support for building without extension even when compiler
is functional, and set up extension-less travis builds.

Allow the compilation of the extension to fail, and switch
to pure python mode.