* Initial smallz4 support, related to #19849
* Patch smallz4 to return -1 on error (as opposed to just exit)
* Add new function 'unlz4Block_userPtr' that can decompress an lz4 block
* New '--with-smallz4' flag to compile and use smallz4 instead of lz4
* Reuse the new unlz4Block_userPtr function to remove duplicate code from unlz4_userPtr in smallz4
* smallz4: remove patch, format small4cat.c properly