Implement glob ignores (#272)

* Add Glob wrapper type with better serialization

* Introduce PathIgnoreRule struct

* Implement equality for Glob type

* Add PathIgnoreRule to InstanceContext

* Implement glob ignores in directory middleware

* Fix up filters

* Use Iterator::all instead of loop

* Add project-level configuration for glob ignores

* Add test project for glob ignores

* Wire up project file and snapshots to make glob ignores work

* Better codepaths for adding ignore rules with empty iterators

* Add test for globs inherited from parent projects

* Add test details, support glob ignores in nested projects

* Add feature flag for globs

* Switch to use ExactSizeIterator instead of size_hint

* Remove glob visitor

rojo-test/build-tests/ignore_glob_inner/default.project.json

@@ -0,0 +1,14 @@
+{
+  "name": "ignore_glob_inner",
+  "tree": {
+    "$className": "Folder",
+
+    "src": {
+      "$path": "src"
+    },
+
+    "subproject": {
+      "$path": "subproject"
+    }
+  }
+}