Merge pull request #120 from yallop/test-header

Add header file for tests to support API-level binding.
Generation of 'external' declarations from types.
Add bigarray support for external declarations.
Basic read/write stub generation support.
Record properties of global names.
C stub generation from types (WIP).
Add ctypes.stubs subpackage.
Rudimentary interface for C_stubs.
Basic code printing (WIP).
Add interface for ml_stubs module.
Printer for generated ML stubs.
Generate function for retrieving primitive constructor names.
WIP
Stub generation tests.