Added zero-padded statepoint names
Wrapped batch number zero padding into a function
Added zero padded filenames for source files

Also correcteted statepoint filenames in write_source_point
Updated tests for zero padded filenames
Commented zero_padded_batch
Merge branch 'develop' into zero_padded_statepoint
Moved zero-padding features to string.F90
Fixed zero_padded error message typo
Fixed overflow error in count_digits
Fixed tests for zero_padded_statepoint
Merge pull request #291 from smharper/zero_padded_statepoint

Batch number on statepoint files are zero-padded