Began api.md documentation

Also changed the responses for /create and /entropy
so that all responses are JSON
began implementing reference client
Merge pull request #60 from dannycoates/docs

API docs and reference client
use old kA on account reset - fixes #59
Merge pull request #61 from zaach/reuse_kA

use old kA on account reset - fixes #59
linked API doc and reference client from readme