Add http handler snippets

[andrewstuart]

This just adds a couple simple snippets for creating http handler functions.

[fatih]

Thanks @andrewstuart 👍

[andrewstuart]

Haha, that was fast! Thanks for keeping up a great project!

[fatih]

Yeap, added it to the changelog as well: https://github.com/fatih/vim-go/blob/master/CHANGELOG.md#17-unreleased

Sometimes the PR's are just simple, so I can merge without any problems. You're welcome and thanks again for the contribution :)

[brunnre8]

what's the reason for not prefixing the ResponseWriter and the Request with http.*?

In my view most people are using the std lib and not developing for it so I expect a handle function to be using the http package

Or am I generally missing something? (I just started learning the language, please be patient 😉)

[andrewstuart]

This should have been fixed by #843 as far as I can tell, and was just an oversight on my part when I created the snippets.