Use configurable path to cpython

Improve comments, rename CLFunction

and a couple of the other related functions:
- addRTFunction is now an overload of FunctionMetadata::addVersion
- boxFunctionMetadata is now createFunctionFromMetadata (it doesn't return a box)
- createRTFunction was just a wrapper around new FunctionMetadata(), so get rid of it
- boxRTFunction is now FunctionMetadata::create

"CLFunction" never really made sense as a name, and some of the other related functions
didn't make sense either (especially after a couple refactorings happened).  Hopefully
this makes it less confusing.

Update head version number to 0.5

update README for 0.4 release

Test PR to track down the travis CI self->map.size() == self->map_elts assert

These cpython tests are passing now

This caused the 'self->map.size() == self->map_elts' assert we saw sometimes on travis CI

Parser fix: call fclose

Misc pyxl2 perf improvements continued

Misc optimizations for pyxl2

Add a FileHandle class for c++-style raii on FILE* objects.

Also, add support for using the cpython parser for parsing
strings (still only in -X mode).

add doc to existed builtin function or method

Support building distribution packages

- Add a pyston micro version
- Move to the convention of "current version number is for the next release",
  instead of "previous release".  I think this is more standard?
- Get rid of our PYTHON_VERSION_MAJOR/MINOR/MICRO flags, and instead use CPython's
  versions.  We in theory had the ability to target different micro versions at
  runtime, but we never made use of this.  Having the two sets of flags isn't
  very sensible either.

Add support for using the CPython parser