Allow {member_id} in member_id parameter to get logged in user

I was in a place where I needed to get the logged in user's member data, however, the {member_id} tag isn't being parsed and therefore returns no results. This allows you to do something like:

    {exp:json:members member_id="{member_id}"}

Because of CI needing to run a query to parse global vars, I had to pull the parsing up before your query happens.