Improve `AbstractMessage#toDomDocument` for XML content.

This changes utilizes the value of the Content-Type header to
determine what the best method is for loading the content into the
DOMDocument.
Properly parse the content type header to extract the format.
cleaned up travis config
allow only http and https protocols by default in curl client
Fixed PSR rules
Added Typed exceptionsAdded Typed exceptions
Fixed Typo, Added marker interface for exceptions
Removed wrong file doc
cleaned up exceptions
added phpunit to composer
Merge pull request #105 from arnaud-lb/allowed-protocols

Allow only http and https protocols by default in curl client
Merge remote-tracking branch 'marijn/feature/xml-aware-to-dom-document'
cleaned up xml detection
moved implements declaration

closes #90
Merge pull request #89 from lyrixx/psr

Fixed PSR rules
Add missing exception change to MultiCurl. Polished phpdoc in FileGetContents. Refactored Client test.
Merge pull request #107 from stloyd/feature/cleanup

Add missing exception change to MultiCurl. Polished phpdoc in FileGetCon...
Support timeouts in milliseconds.

If timeout is less than 1 second, we calculate milliseconds and set
CURLOPT_TIMEOUT_MS option instead of CURLOPT_TIMEOUT.
Merge pull request #108 from p7s1digital/support-timeout-in-milliseconds

Support timeouts in milliseconds for Curl client.
Check for curl version before accessing options