Input params: do not add params to input that were not sent
Change license to MIT
gemspec: fix license
Add action aliases
Default actions: alias new for create
Description: query parameter describe to choose output

If describe is 'versions', list of versions is returned.
'default' returns description of default version, otherwise
all versions are described.
New layout types, new way for resolving action URLs

Layout types: object, object_list, hash, hash_list

Actions now define attribute 'resolve', which is a callable (lambda
or proc) that takes one argument (the instance of the model)
and returns ID or whatever should be put into the URL. Default
implementation returns klass.id, which should serve for most cases.

This commit removes following arguments for I/O params of resource
type: value_params, choice_params
Remove PaperTrail dependency, introduce hooks

Server exposes hook :post_authenticated, which is called after
authentication with the user object as an argument. This hook
may be used to initialize PaperTrail outside HaveAPI.
Base for output formatters, send correct headers

Custom output formatters can now be registered. The input can
be only JSON for now. Check and validate Accept header, send
correctly Content-Type header.
HTML doc: fix content type
Add doc for self-description
Resource param describe: fix URL resolving
Action: allow more examples than one, add title
Add /doc, render with github flavored markdown