Factor out HTTPAdapter.proxy_manager_for for #2048
update AUTHORS.rst
improve `proxy_manager_for` re-usability by subclass
allow pool_kwargs to be specified in init_poolmanager
indentation change for code review
Update out-there.rst

Remove french blog post which is now a deadlink.
Merge pull request #2097 from bkerensa/patch-1

Update out-there.rst
Merge pull request #2049 from codedstructure/adapter-proxy_manager_for

Separated out proxy_manager_for to fix #2048
Update quickstart.rst

line 394: correct an input error.
Merge pull request #2112 from np-csu/patch-1

Update quickstart.rst