Added LaTeX conversion of expressions using toTex() on expression.
Also added some basic tests, which cover some use cases; but should be expanded.
Changed boolean true and false symbols
Allow using symbols in subscript.
Test failed because of missing check of parameter type.
Some tweaks and fixes
Fixed test and removed remaining console.log.
Merge pull request #184 from nheisterkamp/feature/106-LaTeX-toTex

Added LaTeX conversion of expressions using toTex() on expression.