tre-python.c: correct docstring and function name for search().
tre-python.c: support Unicode patterns.
tre-python.c: raise PyErr_NoMem when appropriate.
tre-python.c: support searching in Unicode strings.

Please note that the Unicode string is copied over
and converted to a wchar_t[] before matching.
This is unacceptable for large strings.

TODO: use tre_reguexec to iterate directly over the
Unicode string.