Calculates the MD5 hash of
str using the
RSA Data Security, Inc.
MD5 Message-Digest Algorithm, and returns that hash.
The hash is a 32-character hexadecimal number. If the optional
raw_output is set to TRUE, then the md5 digest
is instead returned in raw binary format with a length of 16.
Note: The optional
raw_outputparameter was added in PHP 5.0.0 and defaults to FALSE