Perform outpatient surgery

This commit features minor optimizations, the addition of NULL to
discard all output when specifying log levels, and justification of
comments.

It should not break any existing implementations, but the previously
named MyOutput() was renamed and made unexported. Any hard-coded
versions of LogLevels such as 0 for EMERG, 1 for ALERT, and so on will
not break, even though they deserve to.
Add unit test for checking prefixes
Flip buggy if statement

Please ignore my half-baked late-night coding decisions.
Improve TestString somewhat
Extremely minor capitalization error
Merge pull request #1 from SashaCrofter/master

Optimizations and minor rewrites