Colors when output is not a TTY

[rudolphfroger]

Currently Cucumber is using color codes even when the output isn't a TTY. For example in Jenkins one can see output like this:

[0m�[1m�[34m[Summary]
�[0m�[0m�[1m�[37m1 features
�[0m�[0m�[1m�[37m1 scenarios (�[0m�[0m�[1m�[32m1 passed�[0m�[0m�[1m�[37m)
�[0m�[0m�[1m�[37m6 steps (�[0m�[0m�[1m�[32m3 passed�[0m�[0m�[1m�[37m)
�[0m

I haven't tried but I can see one place which enforces the use of colors, in macros.rs there's usage of ColorChoice::Always. The termcolor crate gives an example on how to detect the presence of a terminal and set ColorChoice accordingly.

[tyranron]

Resolved in #128