This function allocates memory to hold a C string and fills the
string with the sequence of characters supplied. It then
terminates the string with a null character and returns a
pointer to its start. The memory used for the string may later
be de-allocated using astFreeastFree.
This function is intended for constructing null terminated C
strings from arrays of characters which are not null terminated,
such as when importing a character argument from a Fortran 77
program.