Support templates and capture variables

[divdavem]

It would be good to have support for a template engine, to be able to easily transform a mock into a template, which could include some dynamic variables.
It should be possible to set those variables programmatically from the hook method of the configuration file.
It would also be nice to have an easy syntax to capture with pattern matching some parts of the request (URL, headers, request body) and assign those parts to some variables that can directly be used in the template of the response.