parsing seems to work correctly.
Added a makefile and refactored some of the token parsing inner loop.
Factored out stack functionality into its own data structure.
Factored out operation and token functionality.
Create a symbol predicate function. May be useful if we allow identifiers with any non-alpha characters.
Added floating point recognition for constants. Now, all multiple character tokens must be either T_CONSTANT or T_SYMBOL. Otherwise, T_UNDEFINED is returned, because all other legal tokens are single character tokens.
Factor out tokenization.
Add ability to detect invalid tokens.