Allow post media to work with urls

Currently only works with local files, not useful for tweeting images stored remotely
Update Readme with the line to install by pip
Fix an issue with user streams

* Changed the last loop in GetUserStream to match those in other
  stream functions.
* Check for "Exceeded connection limit for user" messages which come
  with HTTP 420 responses when there are too many connections to the
  Streaming API
Merge pull request #161 from jairot/master

Update Readme with the line to install by pip
Merge pull request #162 from clee704/master

Fix an issue with user streams
Merge pull request #159 from udox/master

Allow post media to work with urls