Separate eval_env and public_bind_env
Migrate R7 into R6, with modular option
Implement super-object creation for R6 modular class
Add R6-modular tests
Remove R7

R7 has been migrated into R6(modular=TRUE).
Formatting cleanup
Check that sub and super-classes are modular or non-modular
Printing tweaks
Merge branch 'merge-r7'