feature API call to download repo archive

defaults to HEAD

Conflicts:
	spec/requests/api/repositories_spec.rb

Change-Id: Id114aca6c59d75f18e49bf9f33809a04e010bfb6
Fix a bug where the tgz returned got encoded utf8

Conflicts:
	doc/api/repositories.md

Change-Id: I7ebc39b47ff860813d9622ba6776583536e6e384
Added more tests for archive api

Change-Id: I2b0752bc2593a944d42dde0ffe0ef9ce408228a5
Remove file compairson

Change-Id: Id2cae87c8cd383bc6cbcbdecf0f77c161bb82eab