Improvements

[SimonHeybrock]

Implements suggestions based on #1.

Checksums are now optional. Example:

notevennexus --checksums DREAM_baseline_all_dets.nxs

Violations
----------
depends_on_missing @ /entry/instrument/endcap_backward_detector
depends_on_missing @ /entry/instrument/high_resolution_detector
depends_on_missing @ /entry/instrument/mantel_detector
depends_on_missing @ /entry/sample
transformation_offset_units_missing @ /entry/instrument/polarizer/transformations/translation

Summary
-------
depends_on_missing: 4/19
depends_on_target_missing: 0/38
float_dataset_units_missing: 0/64
group_has_units: 0/55
index_has_units: 0/15
mask_has_units: 0/0
non_numeric_dataset_has_units: 0/21
NX_class_attr_missing: 0/55
NX_class_is_legacy: 0/55
transformation_depends_on_missing: 0/23
transformation_offset_units_missing: 1/1
units_invalid: 0/64

Total: 5/410
File: DREAM_baseline_all_dets.nxs
Created: 2023-04-20 09:34:50.813815
Modified: 2023-04-20 09:34:23.493762
Size: 1.06 GByte

md5: 1e1a3141c6785d25777b456e2a653f42
sha256: a1af51fc1fe5e5b4ca3ec90acb34f82be14bd39549bd8092db1f71bef89371f2