Annihilates dead code in varea

Code that got moved to classes finally removed (wasn't even being called
for a long time). Varea includes Parsable so it no longer has its own
err methods.

Error is now its own class with a to_s method that takes a boolean to
determine whether or not to print color. #to_pretty is shorthand for
color.

Also all the code that got trimmed is moved to keep_around.rb. It
contains a lot of validations that I don't want to lose until I can
better incorporate them. (specifically cross-section checking)