Log Message:
py-llvmlite: updated to 0.31.0

This release switches memset/memcpy to use the 4 argument style as per LLVM 7+
and updates some documentation.

Commits:
* Revert "Revert "LLVM 7 changed memset intrinsic signature, adjust \ 
it""
* Begin development of 0.31.0
* Add cttz and ctlz to irbuilder docs.
* Update deprecation docs with full deprecation of 5 arg memset/memcpy
* Update docs to not report LLVM 3.8 as latest!