ENH: compare op enum and instr equality

[llllllllll]

This cleans up some rough edges I saw in Jim's codetransformer.

• Makes COMPARE_OP use enums for the input. There are also class level constructors for the different types like: COMPARE_OP.LT
  note: COMPARE_OP.LT is not COMPARE_OP.LT. This means we can use these for equality or take ownership and start jumping to them and so on. The integer enum is COMPARE_OP.comparators.
• Makes the jump instruction constructor manage the _target_of set of the argument.
• Adds a way for subclasses to type check and normalize their inputs.

[jcrist]

This looks good to me. I've been enjoying playing with this - the pattern matching api is very intuitive to use (once I figured out how it works). Thanks for cleaning up some of the rough edges here :)

[llllllllll]

Thanks, I am glad you are having fun with this. I am going to revert the __eq__ change. This makes too many operation abigious. The fact that hash(a) != hash(b) | a == b is a big red flag that this is a bad design. I will instead make an equiv method that checks on type and arguments while still letting == do identity.

[ssanderson]

separate

[ssanderson]

LGTM modulo spelling comment.