Improved Template Parser

[juanluislopez89]

Based on https://github.com/gccloud/parser, this adds to codeigniter template parser class the ability to parse if conditionals, switches, loops, foreachs( with no limit nested arrays), parse array keys and array values and nested array keys and values, helper function calls

[pocketarc]

A couple of initial notes:

1. The Parser_test.php file should be updated to thoroughly test these changes; it should not be in an application-level controller.
2. The user_guide_src/source/libraries/parser.rst file should be updated to document this updated functionality for future users.
3. In addition to these, I'd like to see some support from others (a couple thumbs up on this PR would be nice) before merging it in.