It now uses a plugin registry. Plugins are loaded when the configuration
file is first parsed. When a request is made it is passed over to the
available modifiers before and after it's execution and applies
whichever changes are made. It now passes a copy instead of a reference
to provide a nicer interface.
Dynamic values have been added as a plugin type. These plugins are
javascript functions that can be called from within the beau file and
whose results are used as a replacement.
These are added along with variables to the runtime execution flow. The
current order for their execution is:
Request composition -> Dynamic Values -> Pre-Request Modifiers ->
Post-Request Modifiers.
