Adding custom header in order to provide a POST with a application/x-www-form-urlencoded MIME type.
Adding missing constants
Wiring up the custom http headers for all types of requests
Adding some documentation to the Custom Header Key
Merge pull request #1 from ghvillasboas/develop

Wiring up the custom http headers for all types of requests
Fixing complaints from @toto
Merge pull request #124 from AndreasTextunes/develop

Adding custom header in order to provide a POST with custom MIME types