Update version number to 0.5.2 and update copyright

[paulromano]

Description

This pull request updates the version number to 0.5.2, updates the copyright on all files, and updates the changelog to include a few recent PRs. Once this is merged, I'll tag a new version.

Checklist:

• My code follows the style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have updated the CHANGELOG.md file (if applicable)
• I have successfully run examples that may be affected by my changes