function gets the library version as a string and optionally as an integer
stored in the
argument. If you pass a NULL, no integer is attempted to be returned.
The integer is built up as 24bit number, with 8 separate bits used for major
number, minor number and patch number. This makes a version string such as
1.2.3 will be returned as the hexadecimal number 0x010203 (decimal 66051).