Add dougrain to implementation list

[passy]

Dougrain is a parser and generator implementation of Draft 5 in Python. Not mine, but I like it a lot. :)

[mikekelly]

merged this in but it was already on the github wiki:

https://github.com/mikekelly/hal_specification/wiki/Libraries

the site should definitely link to this page.

[passy]

Yeah, I didn't see the wiki page at all. I added some more JS libraries to that list.

[mikekelly]

awesome, thanks muchly!