Fixed #5 - invalid update of the claimed_id value

Thanks to @alixandru.
Added Composer support.

Thanks to @makasim, @Nodge.
Fixed a warning with a realm shorter than 8 chars
Fix: use cURL if 'allow_url_fopen' is disabled.

Thanks to @mcrumley.
Added ability to set the 'CN_match' SSL option.
Fix: avoid hiding the presence/absence of fields.
Added 'text/html' to the discovery content-types.
Fix: different POST-behavior with cURL vs streams
Minor update, added comments, no logical changes.
Added User-Agent header for better compatibility.
Updated some general project information.
Minor refactoring, no logical changes.
Updated the changelog and the release information