Modify an sds string in-place to make it empty (zero length).
However all the existing buffer is not discarded but set as free space
so that next append operations will not require allocations up to the
number of bytes previously available.
Increment the sds length and decrements the left free space at the
end of the string according to ‘incr’. Also set the null term
in the new end of the string.
Enlarge the free space at the end of the sds string so that the caller
is sure that after calling this function can overwrite up to addlen
bytes after the end of the string, plus one more byte for nul term.
Create a new sds string with the content specified by the ‘init’ pointer
and ‘initlen’.
If NULL is used for ‘init’ the string is initialized with zero bytes.
If SDS_NOINIT is used, the buffer is left uninitialized;
Reallocate the sds string so that it has no free space at the end. The
contained string remains not altered, but next concatenation operations
will require a reallocation.