Upgrade codespell and add custom dictionary

I noticed a bunch of typos while reviewing !169 (merged) and found that the codespell pre-commit hook was quite out of date, so it was missing many typos. I updated it, and also brought in the custom dictionary we had used in the previous version of teklia.com to avoid renaming ourselves to tequila. We never did that here, but better safe than sorry.

This uses a .codespellrc as this means that running codespell in any way (not just via pre-commit) will result in the same configuration being applied all the time.