When attaching buffers to the form, the content type is set to application/octet-stream by default.
Allow the user to set a custom "content-type" when a Buffer is sent.
A new unit test was created to verify that Buffers are being sent correctly and all custom options are taken into account.
Added test for Request. Small fixes.
Removed 0.6 support.
Added custom headers support

Make it possible to send additional customs headers when submitting the
form. Most of the code was already there but it wasn’t used
Added test for the custom header functionality
Documented custom headers option
Updated versions.