Fix binary operator parentheses bug. (#400)

Fixes #399.

Update `test_printers.cpp`:
* Fix compilation and scope management issues, and re-include in CMakeLists.txt.
* Update to use `verbose_print` (run-time verbosity).
* Apply expected output tests to `CPrinter` and `CUDAPrinter` outputs.

Address binary operation rendering issue:
* Move C-style expression rendering common to `CPrinter` and `CUDAPrinter` to a specialized `Visitor`, `CExprRenderer`.
* Use operator associativity to determine need for parentheses around sub-expressions of a binary expression.