Dev Docs: Add REST Documentation

[harding]

Preview: http://dg1.dtrt.org/en/developer-reference#http-rest

This adds documentation for the new REST API in Bitcoin Core 0.10.0. It uses the same formating we use for the JSON-RPC documentation with the section headings formatting based on Twitter's REST docs. (As this is the first REST docs I've written, I looked for examples and liked theirs the most.)

Feedback on content or formatting appreciated.

CC: @jlopp (requested docs in issue #715), @jonasschnelli (did a lot of work on the REST interface)

[jonasschnelli]

Nice work!

• Would it make sense to mention that -txindex needs a -reindex=1? Because from time to time there are question like this: bitcoin/bitcoin#5667.
• Maybe it would be good to tell the users once again that they should NOT allow public access to the bitcoind http/rest server

ACK.

[harding]

@jonasschnelli good ideas! I'll make both those changes momentarily. Thanks for your review!

[jlopp]

ACK

[harding]

Commit 73eb097 adds both notes suggested by @jonasschnelli, adding them to the relevant parts of both the REST and JSON-RPC docs. Preview updated.

In the absence of critical feedback, this pull will be merged around 20:00 UTC Tuesday.