Minimalistic reply REST HTTP server.

This implements a minimalistic repl REST server as well as a naive connection pool.

When started with learning enabled will learn from input text
otherwise will be in read only mode.

Currently the only endpoint avaiable is '/<brain>/reply'. To get a
reply POST plaintext to this endpoint. Replies are just plaintext,
too.

One or multiple brains must be specified when starting the server.
This protects against arbitrary creation of brains while also
allowing to switch brains on a per request basis (i.e. to support
multiple languages).