Closes #27. Operator methods

[faultyserver]

Most operators are now allowed as method names. The supported list is: +, -, *, /, %,
<, <=, !=, ==, >=, >, [], and []=. The last two are not operators that are recognized by the lexer, but rather operators that the parser infers from the access and access assignment syntaxes.

An interesting effect of the implementation is that the operators can be defined statically or on modules and still have the same effects:

 deftype Foo
  defstatic +(other)
    :called_op_on_type
  end
end

Foo + Foo #=> :called_op_on_type

This has the potential of being used for some type algebra and/or metaprogramming. I don't really understand the extend of what it could do, but I'm glad it works nonetheless.