Pass a context to the evaluator

When evaling ruby config, pass the original caller
in to be checked in method_missing. This fixes
RiotGames/ridley#202
cleanup methods, call it caller not ctx
spec
Merge branch 'fix_ridley_202' into fix_berkshelf_808

Conflicts:
	lib/buff/config/ruby.rb
s/caller/context/
spec

Merge branch 'fix_ridley_202' into fix_berkshelf_808

Conflicts:
	lib/buff/config/ruby.rb