feature: listing all tasks defined by -desc(...)

[andrzejsliwa]

goal:

list all tasks defined by -desc():

-desc("some desc") ->
some_task(_Args) ->
     ...
     ok.

...

$ ./eake -T

some_task -        some desc

output could be coloured using ansi and format similar to rake:

example:

./eake about                                    # List versions of all Rails frameworks and the environment
./eake airbrake:deploy                          # Notify Airbrake of a new deploy
./eake airbrake:heroku:add_deploy_notification  # Install Heroku deploy notifications addon

with full filling with spaces to longed task name