Add missing godoc comments for collection.go
Add missing godoc comments for collection.go

Change-Id: I76cb67b7b19f977cd7beeac651f10457d535bcc0
Reviewed-on: http://review.couchbase.org/77089
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>
Tested-by: Sundararaman Sridharan <333a3f71d3ad6e01fc953c4fa06bc1f3cd014910@couchbase.com>

steveyen/moss,steveyen/moss,couchbaselabs/moss