Add infrastructure

Add several tools to help with the extension development:

- 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.

Change-Id: I2395556113649ee0221a61a4a7966492bbdad8e8
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..99bc392
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+out/
+src/manifest.json