lang: parser, funcs: Take out the built-in history function

It's a normally named function for now, until we think of a common
package to move it into.

Hopefully this makes improving the lexer and parser easier for now. We
can consider bringing it back if needed.

examples/lang/history1.mcl

@@ -2,7 +2,7 @@ import "datetime"
 
 $dt = datetime.now()
 
-$hystvalues = {"ix0" => $dt, "ix1" => $dt{1}, "ix2" => $dt{2}, "ix3" => $dt{3},}
+$hystvalues = {"ix0" => $dt, "ix1" => history($dt, 1), "ix2" => history($dt, 2), "ix3" => history($dt, 3),}
 
 file "/tmp/mgmt/history" {
 	state => $const.res.file.state.exists,