Bugfix/optimisation release

What's Changed

• Refactor/stocks data as pdseries by @fmilthaler in #92
• Chore/pylint by @fmilthaler in #96
• Chore/pypi cd by @fmilthaler in #98
• Chore/pylint improvements by @fmilthaler in #100
• Adding new stage for the CI workflow: running pylint on code base by @fmilthaler in #101
• minor bug fix (.iloc[i] instead of .loc[i]) and optimization on portfolio by @fmilthaler in #32

Thanks to @donin1129 for the bugfix and optimisation

Full Changelog: v0.3.0...v0.3.1