Fix a warning with Content-Type in ToolbarListener

A class HttpHeader don't have a magic method __toString() in version
2.0.*. We need to call a method like toString() or getFieldValue()
instead. fixes #43
Fix minor spelling errors
Fix and update PhpDoc comments
Merge pull request #44 from b-durand/hotfix/check-content-type

Warning in ZendDeveloperTools/Listener/ToolbarListener.php
Merge pull request #45 from localheinz/hotfix/spelling-errors

Fix minor spelling errors
Merge pull request #46 from localheinz/hotfix/php-doc-comments

Fix and update PhpDoc comments
Change single quotes to ticks
Merge pull request #47 from localheinz/hotfix/readme

Change single quotes to ticks
Add rule to ignore OSX finder and PhpStorm, Netbeans and Zend Studio project files
Merge pull request #49 from localheinz/feature/add-gitignore

Add rule to ignore OSX finder and PhpStorm, Netbeans and Zend Studio pro...