Add generic names in datasets section with regex

[jmorice91]

When you want to write the following dataset 'group${index}/array_data'

write:
   array_data:
     dataset: 'group${index}/array_data'
     dataset_selection:
        size: [ 3, 8]
        start: [0, 0]
     memory_selection:
        size: [ 3, 8]
        start: [1, 1]

In previous version of pdi, you needs to define a dataset in the datasets section for each index:

datasets:
  group001/array_data
  group002/array_data
       :
  group999/array_data

This fix allows to define one generic dataset in the datasets section using regex:

datasets:
  group.*/array_data