Withdraw the obsolete PEP 395
Withdraw the now obsolete PEP 406
Fix PEP type for PEP 453
Withdraw my faster stdlib updates PEP
First draft of standard metadata extensions PEP

This is part of a larger refactoring of PEP 426, but I needed
to commit this early in order to claim the PEP number and
cross reference it from PEP 426 and 440.
Major update to metadata 2.0 draft specs

- split many fields out to standard extensions
- support for local versions in PEP 440
- addressed several other issues noted in
  https://bitbucket.org/pypa/pypi-metadata-formats/issues