Add `ConfigFile` for evaluating Sanford config files

This adds the logic for evaluating Sanford config files. This will
be used to "choose" which server you want to run via the Sanford
CLI. These files work in a similar manner to Rack's rackup files.
The file expects `run` to be called with a Sanford server. The
CLI will then use the server to either start a process or send
a signal to an existing process.

This also renames the `Server` in `test/support` from `TestServer`
to `AppServer`. This is to avoid collisions with the usage of
`TestServer` in unit tests that rely on a server. I don't want to
accidentally couple these unit tests to this server or alter the
server so that the system server tests start breaking in strange
ways.
Merge pull request #124 from redding/jcr-config-file

Add `ConfigFile` for evaluating Sanford config files
`TestRunner`, dependency inject attributes on service handler

This adds dependency injecting attributes on service handlers
with the `TestRunner`. This allows passing more than just params
when using the `test_runner` test helper. The `TestRunner` now
takes a hash of args and it will pull out keys for params, logger
and a request. Any other keys in the hash will be used to try and
write their values to the service handler it builds. This allows
dependency injecting values when a handler is built.

This also changes `Runner` to no longer have an `init` and `init!`
methods. These were originally done when `Runner` was a mixin that
could be used and configured on servers. This is no longer the case
and they were only used by the test runner so there's really no
need to keep these methods.

This also moves the serializing of a response. It is now done
whenever the test runner builds a response, either from initing
or running the service handler, not just when its run. This makes
sure that when a handler halts in its `init!` or a callback, we
also try to serialize these responses to ensure they don't throw
any errors.

Finally, this adds unit tests for the test runner. Previously it
was only tested implicitly via the service handler.