Refactor generateManifest infra tool

- Changed from using bash/perl to using go.
- Now "if" statements in .gjson files can be stacked, and there can be
  conditional "or" statements inside, like |#if defined(A || B)|.
- Go tests were added to make sure that the generateManifest tool
  continues to work as expected.
- Updated docs to reflect the fact that the manifest is now generated
  with a different tool, and Go is now required in the build phase.

Change-Id: Id866d1a49a7ab4aac2dcf8d188c56bb8254a80de
diff --git a/release.bash b/release.bash
index 75ac4aa..269bd4d 100644
--- a/release.bash
+++ b/release.bash
@@ -64,9 +64,9 @@
 # First of all, generate the appropriate manifest.json file for the
 # target browser
-bash generateManifest.bash "${dependencies[@]}"
+go run generateManifest.go "${dependencies[@]}"
 # This is the version name which git gives us
 version=$(git describe --always --tags --dirty)