Interrupt instead of killing on stop by default

The former behavior was causing invalid cleanup for some services. This
change allows the stop signal to be configured through the :stop-signal
option.
Merge branch 'interrupt'
Derive prodigy-mode from special-mode.
Improve clean up.
Use view mode in process output buffers.
Add env property.

Used to temporarily set environment variables when starting process.
Merge branch 'env-property'
Move test helpers.
Override service with same name if exists.
Return nil in prodigy-define-service.
Add color to status.
Add support for tag filters.
Then I should see services should match exactly.
Add support for name filters.
Merge branch 'filters'
Release v0.1.0.
Simplify scenarios using external servers.
Insert new process output at end of buffer.

While preserving current position.
Require cl in tests.
Do not support Emacs 23.