* cretonne-faerie: add a translation mechanism for LibCalls
* cretonne-faerie: docs for libcall_names, rustfmt
* cretonne-faerie: switch libcall naming to use a closure
* travis: debug mypy version
* travis: pin mypy to 0.521
mypy released 0.600 today and even with `--no-strict-optional` flag
passed to it (in lib/codegen/meta/check.sh) it fails to infer the type
of values that did not need type annotations in the past
* faerie-backend: fix swapped nearbyint functions
* cretonne-faerie: move boxing out of FaerieBuilder
69468915d5