Add nix crate, use it for signaling

Cargo.lock

@@ -912,6 +912,7 @@ dependencies = [
  "md-5",
  "minecraft-protocol",
  "named-binary-tag",
+ "nix",
  "notify",
  "pretty_env_logger",
  "proxy-protocol",
@@ -981,6 +982,15 @@ version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
 
+[[package]]
+name = "memoffset"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5de893c32cde5f383baa4c04c5d6dbdd735cfd4a794b0debdb2bb1b421da5ff4"
+dependencies = [
+ "autocfg 1.1.0",
+]
+
 [[package]]
 name = "minecraft-protocol"
 version = "0.1.0"
@@ -1090,6 +1100,20 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "nix"
+version = "0.26.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46a58d1d356c6597d08cde02c2f09d785b09e28711837b1ed667dc652c08a694"
+dependencies = [
+ "bitflags",
+ "cfg-if 1.0.0",
+ "libc",
+ "memoffset",
+ "pin-utils",
+ "static_assertions",
+]
+
 [[package]]
 name = "notify"
 version = "4.0.17"
@@ -1574,6 +1598,12 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "static_assertions"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
+
 [[package]]
 name = "strsim"
 version = "0.10.0"