Merge pull request #16 from wagnert/master

Add new header constants
Merge pull request #17 from wagnert/master

Bugfix for missing comma
added error message rendering
Merge branch 'master' of https://github.com/techdivision/TechDivision_Http
corrected method docblock
Merge pull request #18 from zelgerj/master

added error message rendering feature
Add HttpRequest::getVersion() and HttpResponse::
removeHeader($name) methods