Typing: Narrow down types of arguments (NDFrame)

[kevinanker]

• closes parts of # 10 (in https://github.com/noatamir/pydata-workshop)
• All code checks passed.
• Added type annotations to new arguments/methods/functions.

Updated item 11-14 (15 seemed already done):

• Specify method in to_sql more precisely
• Specify errors in to_csv more precisely
• Specify mode in to_csv more precisely
• Specify kind and na_position in sort_values more precisely

[kevinanker]

@phofl @noatamir

[noatamir]

Thanks for the PR @kjanker! There are a couple of errors identified by pre-commit, which I think you can solve yourself. Let me know if you need help understanding the errors.

[twoertwein]

Thanks @kjanker!