Normalize names in a URL

PyPI and Bandersnatch now normalize the project name in their
URLs. This change matches that and will reduce the number of
redirects we hit on PyPI and will reduce the need to hit /simple/
on a Bandersnatch mirror.
delete two unused functions
update changelog entry for PR 1838
reverse the deprecation of --build and --no-clean
Merge pull request #2001 from dstufft/normalize-URLs

Normalize names in a URL
Do not look for /simple/{name}/version/ URLs anymore
Deprecate the fallback to /simple/
InstallRequirement.absolute_versions is no longer required.
Merge pull request #2064 from dstufft/pr-2062

reverse the deprecation of --build and --no-clean
Merge pull request #2046 from dstufft/simplify-simple-urls

Simplify simple urls
Merge pull request #2055 from bukzor/buck-del-unused-functions

delete two unused functions
Use encrypted vars instead of branch names to stop forks from notifying
Merge remote-tracking branch 'upstream/develop' into buck-found-versions