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.
Point at freezegun master since PR has been merged
Merge pull request #2052 from dstufft/freezegun-master

Point at freezegun master since PR has been merged
delete two unused functions
just the @cached_property bit
Merge pull request #2058 from bukzor/buck-cachedproperty

just the @cached_property bit
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
.gitignore: add .sw[a-z] files

for ViM swap files
unpack_url: session only needed for unpack_http_url
vcs: add documentation to VersionControl class