feat(subscriptions): add and remove subscribers

This commit adds two new commands to add and remove subscribers to
WindowManagerEvent and SocketMessage notifications after they have been
handled by komorebi.

Interprocess communication is achieved using Named Pipes; the
subscribing process must first create the Named Pipe, and then run the
'add-subscriber' command, specifying the pipe name as the argument
(without the pipe filesystem path prepended).

Whenever a pipe is closing or has been closed, komorebi will flag this
as a stale subscription and remove it automatically.

resolve #54

README.md

@@ -276,6 +276,8 @@ start                         Start komorebi.exe as a background process
 stop                          Stop the komorebi.exe process and restore all hidden windows
 state                         Show a JSON representation of the current window manager state
 query                         Query the current window manager state
+add-subscriber                Subscribe to all komorebi events on a named pipe
+remove-subscriber             Subscribe to all komorebi events on a named pipe
 log                           Tail komorebi.exe's process logs (cancel with Ctrl-C)
 quick-save                    Quicksave the current resize layout dimensions
 quick-load                    Load the last quicksaved resize layout dimensions
@@ -393,6 +395,7 @@ used [is available here](komorebi.sample.with.lib.ahk).
 - [x] Helper library for AutoHotKey
 - [x] View window manager state
 - [x] Query window manager state
+- [x] Subscribe to event and message notifications
 
 ## Development
 
@@ -450,3 +453,34 @@ representation of the `State` struct, which includes the current state of `Windo
 
 This may also be polled to build further integrations and widgets on top of (if you ever wanted to build something
 like [Stackline](https://github.com/AdamWagner/stackline) for Windows, you could do it by polling this command).
+
+## Window Manager Event Subscriptions
+
+It is also possible to subscribe to notifications of every `WindowManagerEvent` and `SocketMessage` handled
+by `komorebi` using [Named Pipes](https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes).
+
+First, your application must create a named pipe. Once the named pipe has been created, run the following command:
+
+```powershell
+komorebic.exe add-subscriber <your pipe name>
+```
+
+Note that you do not have to incldue the full path of the named pipe, just the name. If the named pipe
+exists, `komorebi` will start pushing JSON data of successfully handled events and messages:
+
+```json lines
+{"type":"AddSubscriber","content":"test-pipe"}
+{"type":"FocusWindow","content":"Up"}
+{"type":"FocusChange","content":["SystemForeground",{"hwnd":1443930,"title":"komorebi – README.md","exe":"idea64.exe","class":"SunAwtFrame","rect":{"left":1539,"top":60,"right":1520,"bottom":821}}]}
+{"type":"MonitorPoll","content":["ObjectCreate",{"hwnd":2624200,"title":"OLEChannelWnd","exe":"explorer.exe","class":"OleMainThreadWndClass","rect":{"left":0,"top":0,"right":0,"bottom":0}}]}
+{"type":"FocusWindow","content":"Left"}
+{"type":"FocusChange","content":["SystemForeground",{"hwnd":2558668,"title":"Windows PowerShell","exe":"WindowsTerminal.exe","class":"CASCADIA_HOSTING_WINDOW_CLASS","rect":{"left":13,"top":60,"right":1520,"bottom":1655}}]}
+{"type":"FocusWindow","content":"Right"}
+{"type":"FocusChange","content":["SystemForeground",{"hwnd":1443930,"title":"komorebi – README.md","exe":"idea64.exe","class":"SunAwtFrame","rect":{"left":1539,"top":60,"right":1520,"bottom":821}}]}
+{"type":"FocusWindow","content":"Down"}
+{"type":"FocusChange","content":["SystemForeground",{"hwnd":67344,"title":"Windows PowerShell","exe":"WindowsTerminal.exe","class":"CASCADIA_HOSTING_WINDOW_CLASS","rect":{"left":1539,"top":894,"right":757,"bottom":821}}]}
+```
+
+You may then filter on the `type` key to listen to the events that you are interested in. For a full list of possible
+notification types, refer to the enum variants of `WindowManagerEvent` in `komorebi` and `SocketMessage`
+in `komorebi-core`.