Closes #82

Closes #37
Closes #36

* Fix Unicode issue #26 for Python 3 files.

* Refactor tests
 - Make it easier to test against other packages

* Split out optional tests and use assertXXX naming conventions

* Fix Python 3 test intrapackage import

* Fix Python 3 test intrapackage import

* Enhance code generator performance
- Algorithmic gains in pretty printer and string prettifier
- Diminishing gains from a few closures in code_gen
- One code-gen fix (and a test case) for None leaking into code-gen result list.
- rtrip gains via new fast comparison function
- PEP8 fixes

* Fix new deprecation warnings
  - Change to DeprecationWarning to reduce noise in other testers
  - Set stack level so warning appears with proper source line
  - Check for warning in test

* Explicitly verify warning content

  - Bonus:  works with all testrunners.

  -  We already pass these, but some other unparsers don't,
     so it's worth adding them to the regression.

Add support for __future__ unicode_literals

  -- This only affects a very few modules that did not roundtrip properly

Deprecate old API (issue #59)

Dual docs -- issue #63

  - Plus add more verbose changelog format as suggested by Berker

Add support for ASTs compiled with single or eval options

- Clean up code providing new functionality
- (Thanks  for the initial functionality, Ryan) 👍 
- run extended test cases via astor.rtrip
- add regression tests for new features based on rtrip failures
- fix failing regressions

Otherwise, pretty printer will think it can break them up, and no joy
will come from that.