Response and Request objects are pickleable.

Includes a basic test. More could be add to confirm known attributes
that could cause problems.
Add target to build the documentation
wording
issue #1746 : Don't lowercase the whole URL!
use geturl to lower scheme
Merge pull request #1733 from ionrock/pickleable-responses

Response and Request objects are pickleable.
Merge pull request #1742 from kevinburke/docs

Add make target to build the documentation
Merge pull request #1747 from daftshady/lowercase

#1746 don't lowercase the whole url