Added support for custom urlencoded parsers

[AlexMeah]

We are looking for a way to pass custom options to the urlencoded parser, this has previously been denied due to qs being deprecated #98.

Would this solution to allow custom parsers be something you'd be open to?

[dougwilson]

Hi @AlexMeah , I think the idea is in the right direction :) Instead of baking it in to be specific to the urlencoded parser, it would probably benefit a wider audience (including your use-case, to implement something more general, in line with the #22 idea. Some relevant conversation in #42

[AlexMeah]

@dougwilson I'll hopefully get some time this week to make the changes

[dougwilson]

Cool :) ! I started this work a while ago, on the 2.x-refactor branch (https://github.com/expressjs/body-parser/tree/2.x-refactor) so you'll probably want to use that as a starting point to build it. The idea is that the module will simply be a pluggable generic parsing module and then the 4 parsers that already exist will simply all directly use the generic parsing (kind of like eat your own dog food: if all the existing parsers are just using the generic one, then it's a good indicator that the generic one is really generic and is a good base for everyone to use).