newLen
Creates a new #GString with @len bytes of the @init buffer. Because a length is provided, @init need not be nul-terminated, and can contain embedded nul bytes.
Since this function does not stop at nul bytes, it is the caller's responsibility to ensure that @init has at least @len addressable bytes.
Return
a new #GString
Parameters
init
initial contents of the string
len
length of @init to use