initial encoder class implementation with code assignment step

encoder class takes RPN list from translator and assigned codes to
tokens without codes (for now just constants and variables)

constant, variable and variable reference codes added to table for each
data type with has operand flag to indicate these codes will have an
operand word after the instruction word in the program

new streamlined findCode() function added to table that sets the code of
the token, the type of the token to the type of the code, and calls the
full findCode() function

modified token text to output token string after code if code has an
operand (flag of code is set)

added encoder command line test modes, used 'c' for 'encoder' since 'e'
is already being used for 'expression'; modified test scripts to include
encoder testing; added simple initial encoder test for initial debugging