Add infrastructure

Add several tools to help with the extension development:

- Add .editorconfig file to set formatting options for the code editors.
- Add generateManifest.bash to generate the manifest.json file
  dynamically, from a template at templates/manifest.gjson. The
  manifest.gjson file can have lines defining what parts of the manifest
  are added for each target browser.
- Add release.bash to generate the extension ZIP files.
- Add Makefile to serve as a wrapper for the release.bash script.
- Add tagRelease.bash to help tag versions in Git accordingly.
- Add docs to explain all this new infrastructure (will need to be
  updated in the future with more details).

Change-Id: I698ffc59d0d2ec02b483935f7860e95760951a42
diff --git a/generateManifest.bash b/generateManifest.bash
new file mode 100644
index 0000000..eaea8aa
--- /dev/null
+++ b/generateManifest.bash
@@ -0,0 +1,2 @@
+genmanifest -template templates/manifest.gjson -dest src/manifest.json "$@"