Support CMake 3.3+

I guess our hack for pre-3.3 doesn't work in 3.3, but thankfully
we can include both the pre-3.3 workaround and the actual 3.3+ fix,
and it looks like cmake will end up doing the right thing in both cases.

modified git_svn_gotorev.py to work with both py2 and py3

Move the sqlalchemy 0.5 test to extra/

Use configurable path to cpython

This removes it from the debug testing configuration and should hopefully
reduce CI timeouts.

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