#6 Add String to savegame format helper functions

[Grant McDorman]

A number of MWSE scripts go through some convolutions to have strings saved in the player's saved games. Typically, the string is written to a file (xFileWriteString), and then read back as a number of long values (typically 16).

Helper functions to facilitate this (without requiring a file) should be added; something like
<length>, <long1>, <long2>, ... <long16> xStringToLong <string>
<string> xLongToString <length>, <long1>, ... <long16>
An alternative is to have the string-to-long function return a single long, given an offset, and long-to-string to append to an existing string. In the latter case, the string-to-long would return zero when the offset was at or beyond the end of the string, and the long-to-string would do nothing when the value was zero.