Simplify resume freezing; avoid transformations on foreign fields. Fixes#198
but needs followup to allow users to specify how and when freezing, encoding,
and transformations occur.
(1) AbstractResume adds complexity without contributing utility. There's not
really a clean "class" abstraction in JavaScript to begin with; CoffeeScript
classes, as nice as they are syntactically, occlude the issue even further.
(2) AbstractResume currently functions as a container for exactly two functions
which arguably should live outside the resume class anyway.
Remove file-based open methods from resume classes; force clients to use
clean string-based or JSON overloads; fix processing glitch in
validate(); tweak outputs; adjust tests; update CHANGELOG; etc.
