Visit load store / exception framework

[daviis]

I have implemented enough to get the scope working with variables in a test file both loading and storing. If there is a variable in scope already and it gets reassigned with a new type then an exception is raised. These exceptions are in the new file Exceptions. I also went back to some of the older parts where we were just printing to sys.stderr and replaced them with exceptions.

Also made visitgeneric not excede recursion depth and print out the name that needs a visit* added for it. Upon reflection I was very wrong about this not being necessary, so I fixed it.

[JakeAlbee]

Looks very solid with good logic. Passed all the tests I tried