Add Composer.json for Thrift 0.9.1 release

The 0.9.1 release is missing composer.json.
This patch applies the same composer.json from branch 0.9.x into branch 0.9.1

I do not know if it is safe to force the 0.9.1 tag to include this commit, or if a "0.9.1a" approach is feasible.