Support for null checks.

Changed the way that the values are transformed.
Supporting literal for grammar/condition building.
Improved docs.
Moved value transformation to translator.

 - Added documentation
 - Changed regex to be case sensitive
Merge branch 'austint' of https://github.com/austint/agave into condition-redux
Updated README; created new test file for new date util
Changed weekdayToNumberConverter function to be case insensitive, and modified syntax of conditional statements.