1) There's now a .fops pointer that can be set in the context creation info. If set, the array of
fops it points to (terminated by an entry with .open = NULL) is walked to find out the best vfs filesystem
path match (comparing the vfs path to fops.path_prefix) for which fops to use.
If none given (.fops is NULL in info) then behaviour is as before, fops are the platform-provided one only.
2) The built in fileserving now walks any array of fops looking for the best fops match automatically.
3) lws_plat_file_... apis are renamed to lws_vfs_file_...
