Change Mom to SlotMachine

rather large commit, but essentially a simple rename
Rationale in docs and blogs

lib/slot_machine/macro/exit.rb

@@ -0,0 +1,10 @@
+module Mom
+  class Exit < Macro
+    def to_risc(compiler)
+      builder = compiler.builder(compiler.source)
+      builder.prepare_int_return # makes integer_tmp variable as return
+      Macro.exit_sequence(builder)
+      return compiler
+    end
+  end
+end