Warning system, prepare for import stmt, formatting, precommit, spec link, update dev workflow readme section

[zimri-leisher]

Related Issue(s)	#82
Has Unit Tests (y/n)	y
Documentation Included (y/n)	y

---

Change Description

• Add a warning system.
  • Two warnings so far: empty range, and import with side effects
  • Warnings can be ignored or promoted to errors via CLI flags
• Add tests of the import stmt, that are xfail for now. Also add a section to the spec for import.
• Add links between the spec and tests of the spec
• Add a python script which maintains those links
• Add a precommit hook which runs black, and runs the spec linker script
• Reformat the whole codebase with Black
• Update readme developer workflow section to be correct, and also include all the new flags and tools