Changes

Adding OpenACC data directives for mixing length and adg routines

OpenACC structured data regions are added to optimize the data transfers
between CPU and GPU. These data regions will converted to unstrucutred
data region in the later optimization phase.
Results are bit for bit.

Fixing error causing GPU code not to run. Some variables to be copied were labelled as (ngrdcol,nz) when it should be (:ngrdcol,:nz). I've just removed the data length specifiers completely since they are not neccesary in general.