Ignore compiled artifacts by default

Now that the packaging scripts dump files here, these paths can be “officially” ignored.

.gitignore

@@ -1,6 +1,13 @@
+# Rust stuff
 target
-/exa-linux-x86_64
-/exa-linux-x86_64.zip
 
+# Vagrant stuff
 .vagrant
 ubuntu-xenial-16.04-cloudimg-console.log
+
+# Compiled artifacts
+# (see devtools/*-package-for-*.sh)
+/exa-linux-x86_64
+/exa-linux-x86_64-*.zip
+/exa-macos-x86_64
+/exa-macos-x86_64-*.zip