Locates next “token” in a string
a - pointer to token
result - location of occurrence, NULL if not found
This version is different from the system version in that it allows you to pass a read-only string into the function.
This version also treats all characters etc. inside a double quote “ as a single token.
For example if the separator character is + and the string is xxxx+y then the first fine will return a pointer to a null terminated xxxx and the second will return a null terminated y
If the separator character is + and the string is xxxx then the first and only token found will be a pointer to a null terminated xxxx
Not for use in Fortran