Allow grouping of tasks

[tuukkamustonen]

Instead of fab -l giving out something like:

setup                   ...
workon                  ...
clean                   ...
analyze                 ...
test                    ...
run                     ...
doc                     ...
release                 ...
create_env              ...
update_env              ...
delete_env              ...
func_test               ...
perf_test               ...

I would be nice to get:

Initialize:
  setup                   ...
  workon                  ...

 Dev:
  clean                   ...
  analyze                 ...
  test                    ...
  run                     ...

Doc:
  doc                     ...

Release:
  release                 ...

Deploy:
  create_env              ...
  update_env              ...
  delete_env              ...

Test:
  func_test               ...
  perf_test               ...

Namespaces are not a solution to this as:

1. they require also the namespace to be given when invoking tasks (here the tasks are just grouped, they are invoked as before)
2. I don't want to split out my tasks into several files, as my fabfile is already rather simple

Could this be supported through something like:

@task(group='Dev')

Not quite sure how this grouping and namespaces would mix?

[JensRantil]

Proposed new title: Allow grouping when listing tasks. Otherwise we risk mixing up this issue with #1772.

[bitprophet]

This is fixed if you upgrade Invoke to, I think 1.2? It's out in a stable release now either way, check pyinvoke.org. Thanks!