Added Exception support
Begin work on code generation.

    Added truncate function
    Three number token types
Merge branch 'master' of https://github.com/JHoldener/lc3sim
Fixup makefile and includes
Change scanner to only allow registers in range R0-R15
Made PC show proper Hexadecimal Notation
Merge branch 'master' into mac
Update scanner/parser code to reflect master