Rename wiCore to wicore.

Mixed case package names are relatively rare and it could cause issues with case
insensitive file systems.
Make conversion function names coherent
Move all key related code into wicore/key.go
Move all command related code into wicore/command.go
Partial implementation of EventRegistry
Add error instead of panic
Move eventRegistry in its own file in preparation for go generate.

Update git-hooks-go to work with go 1.4.