Add timestamp-based dependency system to build_clib

strip trailing slash from package_dir before counting slashes

Fix usage of extras when installing via Wheels; resolves #882

fixes #935 - allows for glob syntax in graft

Try installing requirements before deploying (because the requirements that tox installed aren't available to the Python that Travis PyPI uses for deployment). Ref #934.

Bundle dependencies instead of vendoring them

Added rudimentary dependency system for build_libraries.
Added obj_deps and cflags keys to build_info dictionary.

Update Python versions