Add example for rawmidi and seq API

[fralalonde]

Also rename existing example to 'pcm' for coherence.

Open to comments, edits, change requests, rejection or plain ghosting.

Here's a sample of the output of the new MIDI example:

--- Raw MIDI devices ---
card_id: "USB" card_name "Pyramid MIDI USB" 
subdevice: 0 "Pyramid MIDI USB MIDI 1" Capture
subdevice: 0 "Pyramid MIDI USB MIDI 1" Playback

card_id: "M37" card_name "Moog Sub 37" 
subdevice: 0 "Moog Sub 37 MIDI 1" Capture
subdevice: 0 "Moog Sub 37 MIDI 1" Playback

card_id: "U4i4o" card_name "USB Midi 4i4o" 
subdevice: 0 "USB Midi 4i4o MIDI 1" Capture
subdevice: 1 "USB Midi 4i4o MIDI 2" Capture
subdevice: 2 "USB Midi 4i4o MIDI 3" Capture
subdevice: 3 "USB Midi 4i4o MIDI 4" Capture
subdevice: 0 "USB Midi 4i4o MIDI 1" Playback
subdevice: 1 "USB Midi 4i4o MIDI 2" Playback
subdevice: 2 "USB Midi 4i4o MIDI 3" Playback
subdevice: 3 "USB Midi 4i4o MIDI 4" Playback

card_id: "P2" card_name "Pro 2" 
subdevice: 0 "Pro 2 MIDI 1" Capture
subdevice: 0 "Pro 2 MIDI 1" Playback


--- MIDI Sequencer Clients, Ports and Subscribers ---
Seq client 128

Client 0 "System"
  Port 0 "Timer"
    READ Addr { client: 142, port: 0 }
  Port 1 "Announce"
    READ Addr { client: 142, port: 0 }

Client 14 "Midi Through"
  Port 0 "Midi Through Port-0"

Client 32 "Pyramid MIDI USB"
  Port 0 "Pyramid MIDI USB MIDI 1"

Client 36 "Moog Sub 37"
  Port 0 "Moog Sub 37 MIDI 1"

Client 40 "USB Midi 4i4o"
  Port 0 "USB Midi 4i4o MIDI 1"
  Port 1 "USB Midi 4i4o MIDI 2"
  Port 2 "USB Midi 4i4o MIDI 3"
  Port 3 "USB Midi 4i4o MIDI 4"

Client 44 "Pro 2"
  Port 0 "Pro 2 MIDI 1"

Client 128 "ALSA_RS_EXAMPLE"

Client 142 "PipeWire-System"
  Port 0 "input"
    WRITE Addr { client: 142, port: 0 }
    WRITE Addr { client: 142, port: 0 }

Client 143 "PipeWire-RT-Event"
  Port 0 "input"

[diwic]

Open to comments, edits, change requests, rejection or plain ghosting.

Hopefully you're also open to having the code merged, because I just did that. :-D Thanks!