Improved query string handling, tests

 - Improved handling of query strings, only set fields will be encoded
 - Added missing fields to streams, channels
 - Added basic tests for streams, channels
 - Made all endpoints that require authentication unexported for now
Added go-querystring library

Query strings are now specified in the ListOptions struct.
In each endpoint we simply need to encode them, a lot less code.
However, go-querystring does not encode bool as 'false' if the 'omitempty'
option is set, instead they are omitted. To get around this we can use
*bool without introducing any more types or changes in the code.
Merge pull request #6 from rojters/bugfix/streams_channels

Improved query string handling, tests