initial float support

they are parsed correctly and you can add them directly with -add, but
it only works in the interactive mode.

compilation fails with a "don't know how to represent" error.
fix variable names
fix rtyping error

somehow rpython can't figure out that m.string has type string, but it
can figure out that m.group(0) is a string.

are there annotations to tell rpython that something is a string? (or
has some specific type in general?)
support adding ints to floats
generate the num ops programmatically
move num op generation closer to protocol definition
fix variable name
Merge pull request #16 from heyLu/add-floats

initial float support (wip)