adding normalizeTrialVariables method

method takes an object (intended to be a trial data structure) and converts any function arguments to their returned value.
First pass at allowing functions as variables
minor bug
Merge pull request #37 from jodeleeuw/master

update branch with master bug fixes
adding normalizeTrialVariables() call to every plugin and plugin template. addresses issue #35
Merge pull request #38 from jodeleeuw/function-variables

Function variables