Release v0.5.1

[btjanaka]

Description

v0.5.1 of pyribs features miscellaneous documentation edits. This PR is part of the deployment steps described in CONTRIBUTING.

TODO

Questions

Status

• [x] I have read the guidelines in CONTRIBUTING.md
• [x] I have formatted my code using yapf
• [x] I have tested my code by running pytest
• [x] I have linted my code with pylint
• [x] I have added a one-line description of my change to the changelog in HISTORY.md
• [x] This PR is ready to go