Add pretty printing to swaymsg

If stdout is a tty, it will pretty print unless -r (--raw) is given.

Sample outputs:

```
~/s/s/build > ./bin/swaymsg fullscreen toggle
Error: Permission denied for fullscreen toggle via IPC

~/s/s/build > ./bin/swaymsg -t get_workspaces
Workspace 3:三
  Output: DVI-I-1
  Layout: splith

Workspace 1:一 (off-screen)
  Output: HDMI-A-1
  Layout: splith

Workspace 5:五 (focused)
  Output: HDMI-A-1
  Layout: splith

~/s/s/build > ./bin/swaymsg -t get_inputs
Input device Metadot - Das Keyboard Das Keyboard
  Type: Keyboard
  Sway ID: 9456:320:Metadot_-_Das_Keyboard_Das_Keyb

Input device Wacom Intuos S 2 Pen
  Type: Tablet tool
  Sway ID: 1386:827:Wacom_Intuos_S_2

Input device Wacom Intuos S 2 Pad
  Type: Tablet pad
  Sway ID: 1386:827:Wacom_Intuos_S_2

Input device Logitech Gaming Mouse G502
  Type: Keyboard, Mouse
  Sway ID: 1133:49277:Logitech_Gaming_Mous

~/s/s/build > ./bin/swaymsg -t get_outputs
Output DVI-I-1
  Geometry: 1920x1080 @ 3840,0
  Scale factor: 1x
  Workspace: 3:三

Output DVI-D-1
  Geometry: 1920x1080 @ 0,0
  Scale factor: 1x
  Workspace: 4:四

Output HDMI-A-1
  Geometry: 1920x1080 @ 1920,0
  Scale factor: 1x
  Workspace: 5:五
```

1 files changed, 1 insertions, 0 deletions

diff --git a/include/sway/ipc-json.h b/include/sway/ipc-json.h
index 02b07a23..3a5af0f5 100644
--- a/include/sway/ipc-json.h
+++ b/include/sway/ipc-json.h
@@ -10,5 +10,6 @@ json_object *ipc_json_describe_bar_config(struct bar_config *bar);
 json_object *ipc_json_describe_container(swayc_t *c);
 json_object *ipc_json_describe_container_recursive(swayc_t *c);
 json_object *ipc_json_describe_window(swayc_t *c);
+json_object *ipc_json_describe_input(struct libinput_device *device);
 
 #endif