Add firestore 2nd gen triggers (#1358)

* adding proposal stuff

* adding basic functionality with complied protos

* pulled out common code into module and added more tests

* added the rest of the tests

* fixing tsconfig

* move protos to root

* update eslint ignore

* adding export things

* add tsdoc strings for dev docs

* add changelog entry

* fix snapshot creation for null docs, add script to protos

* update script

* update readme

* update error message to include datacontenttype

* formatter

Author: colerogers

.eslintignore

@@ -9,3 +9,4 @@ node_modules
 /dist/
 /spec/fixtures
 /scripts/**/*.js
+/protos/

CHANGELOG.md

@@ -0,0 +1 @@
+- Add firestore 2nd gen triggers (#1358).