proper error reporting

[jorenham]

i.e. logging

• [ ] severity levels: debug, info, warning, error, critical
• [x] readable messages for humans
• [ ] consistent error codes
• [ ] option to filter output by severity
• [x] show the location as file:row:col (major IDE's should understand)
• [ ] show the relevant code
  • [ ] color the code
  • [x] mark the precise row/column
• [ ] contextual information such as inferred types and variances and such
• [ ] optional hyperlinks to docs of unpy or python

[jorenham]

loguru might be the way to go here