Add missing cucumber command description

- help
- README.md
Merge pull request #39 from tricknotes/add-missing-command-description

Add missing cucumber command description
Add note about test frameworks
Ensure the file exists before requiring

This will avoid rubygems trying to activate a gem containing the path,
which in a few commits time will make spring faster.
Start to extract spring client commands
Extract help command
put requires where they belong
spring cleaning :lol:
spring does not need to be in the Gemfile
add missing require
Generate binstubs for running spring commands

This solves two problems:

1) It's a bit annoying to prefix every command with "spring". Also you
   don't get autocompletion with "spring t<TAB>".

2) The rubygems load-every-gemspec performance problem
   (https://github.com/rubygems/rubygems/pull/435)

See the changes in README.md for more details.
Set the process title for more informative ps output

Example:

    turnip@mercutio:~/Code/spring/test/apps/rails-3-2:master$ ps ax | grep spring
    23551 pts/3    Sl     0:00 spring server | rails-3-2 | started 2013-02-01 19:59:57 +0000
    23554 pts/3    Sl     0:01 spring app    | rails-3-2 | started 2013-02-01 19:59:57 +0000 | test mode
    23625 pts/3    Sl     0:00 spring app    | rails-3-2 | started 2013-02-01 20:00:01 +0000 | development mode
remove obsolete comment
Server should terminate its children at exit

Closes #40
Update the walkthrough in the README
Make the test command capable of running directories

This makes it a lot more useful for not much effort, so seems worth it.
Don't need to show deprecation warning
README editing [ci skip]
Don't try to kill if pid is nil
Forward signals to running process group

If a command spawns child processes within the same process group, then
they also need to receive the signals.