document Config.Parse
rename parseX to readX

I want to separate those functions into a readX version, which opens a
file and parses the contents, and a parseX version, which only does the
parsing. This will make the parseX function testable.
split parseX from readX
test parseModules instead of readModules

why go through an intermediate file if we can test the pure version.
reorder arguments to favor currying
remove unused import
fix orphan instance
document Hawk.Config