Update printing style

[schneems]

This updates the Procfile to the bullet_stream style of bulletpoint text. The Output has changed to include the command being pulled from the Procfile

[runesoerensen]

I like that this PR adds the Procfile commands to the output, and matches the style of other buildpacks better. The new output drops some of the output that describes what's happening though (and the empty Procfile output seems a bit more awkward).

Current output

// Empty Procfile
[Discovering process types]
Procfile declares types -> (none)

// Procfile defining worker and console
[Discovering process types]
Procfile declares types -> worker, console

New output

// Empty Procfile
## Procfile Buildpack
- Processes
    - (none)
- Done (finished in < 0.1s)

// Procfile defining worker and console
## Procfile Buildpack
- Processes
    - worker: `echo 'this is the worker process!'`
    - console: `echo 'this is the console process!'`
- Done (finished in < 0.1s)

Not a blocker, but would it perhaps make sense to consider ways the new output can retain some of the expressiveness of the current output, and still fit the new style? Maybe something like:

// Empty Procfile
## Procfile Buildpack
- Discovering process types
- Procfile is empty
- Done (finished in < 0.1s)

// Procfile defining worker and console
## Procfile Buildpack
- Discovering process types
- Detected processes
    - worker: `echo 'this is the worker process!'`
    - console: `echo 'this is the console process!'`
- Done (finished in < 0.1s)

or

// Empty Procfile
## Procfile Buildpack
- Discovering process types
    - Procfile is empty
- Done (finished in < 0.1s)

// Procfile defining worker and console
## Procfile Buildpack
- Discovering process types
    - worker: `echo 'this is the worker process!'`
    - console: `echo 'this is the console process!'`
- Done (finished in < 0.1s)