Add new ModularProgram class
Added ModularProgram; updated examples to follow.
remove commented code
Remove more commented code
Added ShaderObject class
Added compiler code from prior system
Closer to working compiler
finished initial changes; starting testing.
Getting closer..
Mesh example works again
line example works again
minor cleanup
Minor edits
revert _template_variables edit
Added comments
revert Function._expressions / _replacements changes
Removed Expression class
Resurrected TextExpression and ShaderObject.create
Updating function tests
finished test_function_changed