Adds more getters to the VirtualMachine (for functions, emitter updaters, bullet updaters).
Adds the implementation of VisitFunctionCallExpression and the tests for it (also rearranges the tests to fit the grammar, again).
Implements VisitParExpressionList and VisitExpressionList.
Fixes up VisitParExpressionList and VisitExpressionList not working correctly.
Updates the design stuff document with some changes I forgot to save a while ago.
Implements VisitReturnStatement.
Adds/fixes some documentation in the HekateScriptVisitor.
Implements VisitBulletUpdaterDeclaration and fixes VisitEmitterUpdaterDeclaration a bunch (was using wrong names, wrong method calls, etc, because of I copy pasted to the wrong method).