Add true and false
Add equality operator
Merge branch 'master' of github.com:nusco/forthr

* 'master' of github.com:nusco/forthr:
  Allow variables to be expanded in composite words
  Removed lookup_table in favor of VariableWord approach
  Add variables implementation
  [Bugfix] Update repl to use new abstracted interpreter class

Conflicts:
	forthr.rb
	forthr_test.rb
Initialize variables to 0

Instead of nil as we did earlier.
0 seems to be gforth's behavior, so it's probably standard.

Also, changed the tests to avoid accessing the interpreter's
internals.
Add one variables test

One more test about expansion.
Probably doesn't add to the existing expansion test, but I'm
kinda paranoid about word compilation because of all the trouble
we had in the past.