Extend power iteration to handle complex Hermitian input matrices

[calvinmccarter]

Describe your change:

This PR extends the standard version of the power iteration to handle complex Hermitian input matrices. The only algorithmic change for complex-valued matrices is that the (simplified) Rayleigh Quotient for finding the eigenvalue needs to use the conjugate transpose (x^H M x) rather than the regular transpose (x^T M x).

I also fixed a typo in the documentation ("eignevalue" -> "eigenvalue").

• Add an algorithm?
• [] Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
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[calvinmccarter]

@cclauss -- I think I fixed the flake8 issue, could you please run the tests again?