lang: Refactor most functions to support modules

This is a giant refactor to move functions into a hierarchial module
layout. While this isn't entirely implemented yet, it should work
correctly once all the import bits have landed. What's broken at the
moment is the template function, which currently doesn't understand the
period separator.

lang/funcs/simple/simple.go

@@ -42,6 +42,12 @@ func Register(name string, fn *types.FuncValue) {
 	funcs.Register(name, func() interfaces.Func { return &simpleFunc{Fn: fn} })
 }
 
+// ModuleRegister is exactly like Register, except that it registers within a
+// named module. This is a helper function.
+func ModuleRegister(module, name string, fn *types.FuncValue) {
+	Register(module+funcs.ModuleSep+name, fn)
+}
+
 // simpleFunc is a scaffolding function struct which fulfills the boiler-plate
 // for the function API, but that can run a very simple, static, pure function.
 type simpleFunc struct {