Merge branch 'regex_linux' into regex

Merged the regex_linux branch to integrate Linux-specific fixes -- namely integration of a -Wtautological-compare fix from master.
Range Unit Tests

Added unit tests for the range construct.
Escape Unit Tests

Added unit tests for the various literal escapes -- i.e. reverse solidus preceded code points/sequences which indicate some other code point.
Atomic Group Unit Tests

Added unit tests for the atomic group structure -- i.e. (?>).