Add optional compression of ajax responses

Implement 'deflate' and 'gzip' encodings and compress flask
response if 'accept-encoding' header is set. Also add alternative
'deflate' method when decoding incoming Readability content.
NOTE: This is probably good for Heroku because GAE, besides
disabling dynamic content generation also seemingly strips
'accept-encoding' headers from incoming requests, probably
because Google guys think they know better when to compress.
On the way, fix some docstrings in lazygen module.