Remove need for "targetLang" declaration for events

[robclewley]

Explore possibility of making zero-crossing event factory functions always create the source code for all possible targets (only 'c', 'python', and 'matlab' are needed anyway, at present). This would avoid needing to require 'targetlang' argument to the factory function, and enable the same event object to be compatible with all suitable target-language Generators. This simplifies the API considerably.