Add support for braced array variables

Created by: huntergoldstein

Problem: While you can express braced string variables, e.g. ${foobar}, you cannot express array variables , e.g. @{zardoz}.

Solution: Add support for braced array variables.

Changes introduced by this pull request:

• Add a braced_array_variable branch for WordIterator
• Allow StatementSplitter to recognize braced array variables
• Extended parser::statements::braced_variable test to also test for braced arrays

Fixes: Closes #262 (closed)

State: Good to go!

Thanks!