Parser: replace regular expressions with a simpler method

[damithc]

Current: regular expressions are used to do the basic parsing of the command

Suggested: use a simpler method

Justification: AB-2 is targetted at students who are just beginning to learn OOP concepts. Regular expressions technique does not match the level of sophistication we can expect from an average student at that level.

[damithc]

In fact, there are multiple places using regular expressions.
I'm requesting this change because I'm using AB-2 in a module where I can't expect students to know/learn regex even at the end of the module and I need to get them started on AB-2 in a couple of weeks.