Added support for automatic functions

[Lucaz97]

This pull requests addresses issue #44 by adding support for automatic functions.

I updated lexer and parser to parse automatic functions. I updated the ast Function object with a boolean attribute 'automatic'. I updated the code generator and the function template to use the automatic attribute to correctly add 'automatic' when generating code for functions. I added 2 tests, 1 for the parser only and one for parser and code generator.

[parker-research]

Looks good to me!