Various improvements:
- Add Cache module
- Add Plot module
- Add deprecation warning to MixedEffectsMatrix
- Remove extraneous print statements from DataMatrix
- Improvements to RBridge
	- Add aov()
	- Allow `memisc()` summary in `lmer()`
- Improvements to TraceJit
	- Add `plotTraceContrast()`
	- Fix `mixedModelTrace()` and make it cachable