Add support for Oriya lR/lRR vowel marks.
Cleaned up comment.
Fix behavior when skipping SGML.

For details, see the new test.
Remove extraneous block

The roman -> Brahmic case was addressed by the previous commit. The
other direction should probably be addressed eventually, but for most
SGML it's safe. (The exceptions are tags that contain Brahmic data.)
Use new $skippingTrans variable in transliterateBrahmic().