Python 3.6 invalid escape sequence deprecation fixes

In upload, infer the username using getpass.getuser()

If m is non-true, then has_mfs must have been False.

A local version label starts with a '+' sign

support dist-info distributions inside zip files

Dropped support for classifiers subsection handling in setup.cfg

 Fix hard link to URLs that should have been internal (method 2: via autosectionlabel Sphinx extension)

Add --skip-dep-install to boostrap.py script

The --skip-dep-install flag skips installation of setuptools dependencies
using pip, delegating this responsibility to other tools.  This can be used to
install setuptools without the need for pip.

closes #950

Add timestamp-based dependency system to build_clib