Detect Parrot assembly and bytecode individually, and add some tests

test/fixtures/hello.pasm

@@ -0,0 +1,5 @@
+#!/usr/bin/env parrot
+
+.pcc_sub :main main:
+    say "Hello!"
+    end

test/fixtures/hello.pir

@@ -0,0 +1,5 @@
+#!/usr/bin/env parrot
+
+.sub 'main' :main
+    say "Hello!"
+.end