Add the option to specify the directory for output files
A few fixes to using an external build_dir

* Copy .hpp and .hh files
* Search for headers recursively
* Don't do anything except for cython sources
copy sources and depends instead of headers
Show attribute access and binary operations in default values in autogenerated signatures.
Attribute docstrings support for cdef public attributes.
Changed bint representation in autodoc signatures from 'int' to 'bool'.
Test fixes for autodoc improvements.
Removed the warning about docstrings for private attributes. Fixed erroneous docstring recognition past the blank line.
Merge pull request #216 from nnemkin/autodoc_improvements

Autodoc improvements
changelog
changelog
suppress warnings about unused error status variables in functions
minor code cleanups
handle some more cases where the error status is known to be used and clean up 'unraisable exception' code
move vtable get/set utility code into ExtensionTypes.c file
use pre-instantiated identifier string when looking up or setting the vtable of exported/imported extension types
move [GS]etVTable utility code to more appropriate ImportExport.c file
fix build
use pre-built Python objects in __Pyx_ExportVoidPtr() utility function
Do not generate tables for completely empty slot suites.