SimpleString::StrStr()

Make it a better strstr()...
Short and sweet...
As per recommendation
Test for SimpleString::StrCmp()
Merge pull request #387 from arstrube/strstr

SimpleString::StrStr()
Rewrite SimpleString::StrCmp()
More tests for SimpleString::StrCmp()
More tests for SimpleString::StrNCmp() modeled after StrCmp()