Replace "int(val) == 0" by "not val" for gdb.Value instances

completed some signatures in Includes - libc.math and numpy.math

Initial Cython patch for Pyston.

rely on code generation phase to include required utility code instead of always including all of it in a separate pipeline phase

Pyston is another Python implementation. More like CPython + JIT. Patch
Cython to add Pyston support.

add "e" and "pi" aliases to libc.math declarations to bring it closer to a drop-in replacement for Python's math module

silence a C compiler warning for trivial generators that do not use their closure class cast (seems to be difficult to avoid such cases)

make new feature-specific guards overridable by user #defines in CPython to allow switching them on and off for testing/debugging/benchmarking

replace generic "COMPILING_IN_*" C macros with feature specific guards that allow a more fine-grained adaptation to C-API implementations