feat: add cli support

.gitignore

tests/input_files/expression.csv

tests/input_files/test.gtf

transcript_sampler/__init__.py

transcript_sampler/cli.py

transcript_sampler/images/.gitkeep

...ript_sampler/images/screenshot_git_tutorial_1_hGillet.png

...ript_sampler/images/screenshot_git_tutorial_2_hGillet.png

...t_sampler/images/screenshot_markdown_tutorial_hGillet.png

transcript_sampler/obsolete_scripts/exon_length_filter.py

...cript_sampler/obsolete_scripts/org_test_representative.py

transcript_sampler/obsolete_scripts/representative.py

transcript_sampler/obsolete_scripts/transcript_extractor.py