1.2.0 numpy interop breaking changes & a lot of re-factoring

This is the last major version supporting Python 2.7. Next major one 1.3.0 will be Python3 only.

• Remove all automatic imports of numpy, and make numpy interop opt-in. By @bennyrowland.
• Move and redefine generating module functions for fixing cross imports. By @junkmd.
• Refactor creating __all__ part in codegenerator.Generator.generate_code. By @junkmd.
• Quit calling GetModule from tools.codegenerator. By @junkmd.
• Commonize module-creating functions. By @junkmd.
• Shorten the lifetime of io.StringIO used for code generation. By @junkmd.
• Fix import source of Array from _ctypes to ctypes. By @junkmd.
• Add for_stub mode to ImportedNamespaces.getvalue. By @junkmd.
• Remove monkeypatch_COMError. By @junkmd.
• Remove CodeGenerator.need_GUID. By @junkmd.
• Carve out CodeGenerator.type_name method to TypeNamer class. By @junkmd.
• Add __known_symbols__ attributes. By @junkmd.
• Remove CodeGenerator.type_name calls no longer needed and rename to _to_type_name. By @junkmd.
• Change _fix_inout_args to module-level top level function. By @junkmd.
• Fix docstring from DispInterfaceHead. By @junkmd.
• ...METHOD and ...PROPERTY return _MemberSpecs instead of tuples. By @junkmd.
• Make generating ...property DRY. By @junkmd.
• Refactor _MemberSpec stuffs and separate modules. By @junkmd.
• Carve out make_...Method and make_...Property of codegenerator. By @junkmd.
• Removed extra space in typeinfo.IRecordInfo._methods_. By @j0ker70.
• Add type annotations to many modules. By @junkmd.
• Fix type annotations in many modules. By @j0ker70, @muddi900, and @junkmd.
• Delint setup.py. By @jaraco.
• Add CONTRIBUTING.md. By @junkmd.
• Modernize README.md style. By @junkmd.
• Add announcements of plan for renaming master branch to main and dropping Python2 to README.md. By @junkmd.