process a text string for options

The optionLoadLine takes two arguments:

1. The pointer to the program's option descriptor (tOptions*).
2. A pointer to a NUL-terminated string that contains a long option name followed, optionally, by a string value.

Leading and trailing white space is trimmed from the value, but otherwise new lines are not discarded. The caller is expected to have NUL terminated the string at the correct point.