Add an interface for running FM scripts

[pilaf]

Currently running FM scripts is supported when saving a record (see FmRest::Spyke::Model::Orm#perform_save_persistence), but not for other actions (delete, search and list). We need to add an interface to allow calling scripts in all those cases, as well as a method for executing scripts directly, which can be accomplished by running a list request with limit 1 (see how this nodejs library deals with it for inspiration).

This may need discussion about the final Ruby interface.

[pilaf]

Addressed in #37 and #38