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

Cargo.lock

@@ -525,6 +525,7 @@ dependencies = [
  "hotwatch",
  "komorebi-core",
  "lazy_static",
+ "miow 0.3.7",
  "nanoid",
  "parking_lot",
  "paste",
@@ -662,7 +663,7 @@ dependencies = [
  "kernel32-sys",
  "libc",
  "log",
- "miow",
+ "miow 0.2.2",
  "net2",
  "slab",
  "winapi 0.2.8",
@@ -692,6 +693,15 @@ dependencies = [
  "ws2_32-sys",
 ]
 
+[[package]]
+name = "miow"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b9f1c5b025cda876f66ef43a113f91ebc9f4ccef34843000e0adf6ebbab84e21"
+dependencies = [
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "nanoid"
 version = "0.4.0"