rgb now handles rgb1 colours, too.
Refactor can_only_be_decimal to use can_also_be_decimal
adding the can_also_be_decimal function
rename `is_decimal` to the more precise `can_only_be_decimal`
Use a hash mark in the hex testrun
Add a testrun script for manual inspection
output to stdout instead of a fixed file
Fix bug: 'hex' was not in HINTS
Remove redundant conversion to int
Add colours_from_rgb1_numbers function
two lines between top-level objects
Create a function to test whether numbers are decimal
Turns out we support hex triplets

Added a test to test this; turns out palette.Color gives us this for free.
Update requirements
Fix the test of rgb colour interpretation
Handle hex invocation
Handle invalid hex colours
Fix error in hex handler
Handle hex colours starting with `#`
Add colours_from_hex_numbers function and test