Added a method to append a time slice to an existing variable:
Assumes variable already created but it can be empty!
Can add single or multiple timesteps
Edit in create_netcdf - time dimension is always unlimited, I've left a comment by this edit in case this breaks something you intended
-bug fix in create_variable dimension called 'time' not 't'
Added method to create empty variable (specify number of dimensions)
Part of #2
Added a method to append a time slice to an existing variable: