[ccan] darray_remove

[Andy Grover]

I was very happy to find darray, but did also need to remove elements 
from the array besides ones at the end. Of course the performance will 
be bad but that's expected. Here it is:

#define darray_remove(arr, i) do {	\
	if (i < arr.size-1)	\
		memmove(&(arr).item[i], &(arr).item[i+1], 
((arr).size-1-i)*sizeof(*(arr).item)); \
	(arr).size--;  \
	} while (0)

It also might be nice to realloc down if size < alloc/2, but this 
doesn't do that.

Regards -- Andy