Added txt format support

This format allows you to get a "plain text" value, i.e. a
untouched copy of the response body.

You can also read not-properly formatted data.

It just adds a xml node named 'entry' with the response body
in wrapped in cdata.
added issues url
Added some documentation

1. Updated the supported format list.
2. Added documentation about the API (prepareGateway and exposeData)
make static calls consistent
timeout is actually in seconds
fixing mix between label and value
Merge pull request #21 from DeuxHuitHuit/timeout

Timeout is actually in seconds
2.1.0 release notes
Merge pull request #22 from DeuxHuitHuit/text

Multiple small fixes
Merge pull request #23 from symphonycms/integration

Release Version 2.1.0