Add @openzeppelin/contracts as alternative package name (#1840)

* Rename package and repository name from docs and scripts

* undo root package rename

* add @openzeppelin/contracts as subpackage with release automation

* synchronize @openzeppelin/contracts version

* remove private field from package.json

* make file patterns absolute

* change wording of a comment

* use a saner version script

scripts/prepare-contracts-package.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# cd to the root of the repo
+cd "$(git rev-parse --show-toplevel)"
+
+# avoids re-compilation during publishing of both packages
+if [[ ! -v ALREADY_COMPILED ]]; then
+  npm run prepare
+fi
+
+cp README.md contracts/
+cp -Tr build/contracts contracts/build