Modifications to hdf and helpers.

Make the types allow arbitary dimension data.
Add a sac module for writing 3D double precision data.
Add an example script.
Changes to field_types to allow writing all the field_types in one call.
Fully working example in 2D and 3D can be read by yt.
First demo of a type independant writing module.
Merge branch 'master' into testing_serial

Conflicts:
	grid_data_format.F90
	helpers_hdf5.F90
Begin work on reading files.
Length independant attribute read.
Add attribure read interface to helpers_hdf
Add read routines to read GDF files.
Read script.
Tidy up the example scripts read to be published.
Merge branch 'testing_serial'
Change layout of repo.