Add parse_level. Fix bug at environment::is_ge

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix bug in level.cpp. Add new example

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix cup symbol. In Emacs, the unicode characters cup and cap are assigned incorrectly.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>