Adding ingest and authentication clients READMEs to the developer docs

Adds automagical updating of READMEs from other repos into CDAP. Pulls down copies from specified versions of files, converts them to rst from markdown, caches the resulting files, and diffs for any changes. If changes are found, it copies the new files so that we know to check in the newly cached versions.
Staged at: http://stg-web101.sw.joyent.continuuity.net/cdap/2.5.0-r2.5.1_ingest_clients/en/tools.html