Implement find, rfind.
Implement find_{first,last}_of and find_{first,last}_not_of.
Added trim(), to minimize memory usage.
Added byte order params to to_utf16 and to_utf32.
Added m_debugStr to UString for debugging help.
Added negative tests to utf8 constructor.
Added fillDeadZone() to update area between
length and capacity.
Added to_string() and cache in UStringRep.