add --help-all meta-switch for recursive help
cosmetical changes to --help-all
possibility to disable calling main if nested_command is called

Compare:

git remote
git remote add
mark commands with color
cli: Fix plumbum switch help text padding
Merge pull request #125 from chaoflow/help-all

Help all, print help for a command and all its subcommands
Merge pull request #126 from chaoflow/option-to-disable-calling-main

possibility to disable calling main if nested_command is called
color program name only on posix and inside a tty

as suggested by @tomerfiliba
Merge pull request #127 from chaoflow/various_small

Various small improvements/fixes