Add CLI arguments.
Add configuration file.
Update zip for unequal data lengths.
Add data loading module.
Refine axis style property specification.
Add rule mark.
Add headless image loading.
Rename vars for consistency.
Add expression parser.
Updates for v1.2.0 release.
Update readme.
Update readme.
Add unit tests for vg.number .
Add unit tests for 'vg.extend' .
Add unit tests for 'vg.duplicate'.
Format source code.
Add unit tests for 'vg.field'.
Merge remote-tracking branch 'upstream/master' into package-test
Add unit tests for 'vg.accessor'.
Add unit test for 'vg.comparator'.