v3.1.3
Only use NO_COLOUR if its value is non-empty! v3.1.3
NO_COLOUR should be respected but only when its value is non-empty.
Previously we just checked if it were present in the environment without checking its value.
See also #15
The env::colour() function is trivial for now but will become slightly more complex when we implement #42.
Full Changelog: v3.1.2...v3.1.3