Addition of MGA projections

[joehealy]

I've probably got the terminology wrong, but I'm wanting to add support for the various Australian grids (MGA - Map Grid of Australia).
http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/geodetic-datums/gda

My (probably not 100% correct) understanding of these is they are based on the GDA94 ellipsoid which is equivalent to the GRS80 ellipsoid.

In doing this, should I add a Geodetics.AUS module, which defines a GRS80 and GDA94 ellipsoid?

Or should the GRS80 one be in a common place as it is likely to be used by other projections?

Secondly, I'm not entirely sure how to handle the various zones of the projections?

For reference, the relevant extract of the proj epsg file is below:

GDA94 / MGA zone 48

<28348> +proj=utm +zone=48 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 49

<28349> +proj=utm +zone=49 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 50

<28350> +proj=utm +zone=50 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 51

<28351> +proj=utm +zone=51 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 52

<28352> +proj=utm +zone=52 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 53

<28353> +proj=utm +zone=53 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 54

<28354> +proj=utm +zone=54 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 55

<28355> +proj=utm +zone=55 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 56

<28356> +proj=utm +zone=56 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 57

<28357> +proj=utm +zone=57 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

GDA94 / MGA zone 58

<28358> +proj=utm +zone=58 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>