Support for form submission multipart/form-data encoding

[tomaszmichalak]

We support only:

• application/x-www-form-urlencoded (the default)
• text/plain

We need to add support for multipart/form-data. In current implementation we throw excetion for header Content-Type="multipart/form-data".

[marcinczeczko]

Looks like vertx 3.4 will provide us all we need in more elegant way. Check Web client in beta version http://vertx.io/blog/vert-x-3-4-0-beta1-release/