WIP: Add script to automatically translate rst docs into any language

[muscache]

This PR introduces tools/translate_docs.py. Run it with a source and destination language and it'll automatically pick up files and translate them through Google Translate.

This script is not stable.

• I haven't figured out how to edit the text in rst nodes. Documentation makes it seem impossible. Until we figure out how to actually substitute the translated text, this script won't be useful
• Integration with sphinx through plugins would be nice to use their .po files approach
• The code lacks tests and is messy
• This approach currently only translates one file at a time, Google can block us for abuse
• No diffing functionality, even unchanged docs will be translated again