finish the documentation

[noah1510]

Now that more languages are going to be added the documentation needs to be more clear and complete.

• document the json formats (-> type_formats.md)
  • combinations.json
  • constatns.json
  • units.json
• document the python data structure
  • document the per unit data
  • document the per target data
• document target specifications
  • add language requirements and considerations
  • add implementation requirement
  • add documentation for the target json format
  • add documentation for target structure
  • add documentation for writing templates
  • add documentation on writing tests