example of variable substitution using environment variables
more precise UnknownCallbackException message
fix wrong tabulation
Merge branch 'develop' into environment-variables-example

Conflicts:
	include/cli/callbacks.hpp
	include/cli/traits.hpp
add parameter substitution to the example. thanks @alu0100693249
Merge branch 'environment-variables-example' into develop
Merge branch 'develop'. Release os-1314c