add tp_finalize slot for Py3.4+
adapt more type structs to Py3.4
use tp_finalize instead of tp_del for Cython generators
move object finalisation code from tp_dealloc() into tp_finalize() in Py3.4
minor code cleanup
fix CPython version checking for tp_finalize()
enable Py_TPFLAGS_HAVE_FINALIZE flag for extension types that need it
use proper C-API function for generator finalisation
minor C code simplification
revert actual tp_finalize() usages, needs more thought
fix CPython version check for tp_finalize()
Cleanup unneeded cpdefs and public declarations.

Per Stefan's comment these are unneeded and actually the tests still pass.
Removed directive_type for gc_no_clear as it can be inferred.
disable PyPy build on travis - takes way too long
Merge pull request #248 from Bluehorn/master

no_gc_clear implementation (disable tp_clear) + doc and tests
Merge pull request #233 from vitek/_type_inference_new

Assignmment based type inference
remove outdated comment
make the NULL-instead-of-None change in tp_clear() optional and off by default - breaks too much code for now
extend no_gc_clear test to check closures for their automatic tp_clear() behaviour
fix docstring reuse from distutils Extension base class