Run Purescript 0.12 parallel to 0.17

pulp12

#!/bin/bash

cp ~/.local/bin/purescript/v0.12/purs ~/.local/bin/purs
pulp $@
rm ~/.local/bin/purs

# - still got purs 0.11.7 from npm
# - have current purescript/purs compiled/installed with stack
# - move the version somewhere (I opted into the path above)
# - have .local/bin before your npm installed bins in your PATH
# - have the script above in ~/.local/bin as well and make it executable
# - now I can just do `pulp12 ...` do use builds for *purs 0.12*