hashmap and serialization

not sure about the messagepack format, but its fine for now.

Cargo.lock

@@ -235,6 +235,8 @@ name = "image-similarity"
 version = "0.1.0"
 dependencies = [
  "image",
+ "rmp-serde",
+ "serde",
 ]
 
 [[package]]
@@ -368,6 +370,12 @@ version = "1.16.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "86f0b0d4bf799edbc74508c1e8bf170ff5f41238e5f8225603ca7caaae2b7860"
 
+[[package]]
+name = "paste"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1de2e551fb905ac83f73f7aedf2f0cb4a0da7e35efa24a202a936269f1f18e1"
+
 [[package]]
 name = "pin-project"
 version = "1.0.12"
@@ -442,6 +450,28 @@ dependencies = [
  "num_cpus",
 ]
 
+[[package]]
+name = "rmp"
+version = "0.8.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44519172358fd6d58656c86ab8e7fbc9e1490c3e8f14d35ed78ca0dd07403c9f"
+dependencies = [
+ "byteorder",
+ "num-traits",
+ "paste",
+]
+
+[[package]]
+name = "rmp-serde"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c5b13be192e0220b8afb7222aa5813cb62cc269ebb5cac346ca6487681d2913e"
+dependencies = [
+ "byteorder",
+ "rmp",
+ "serde",
+]
+
 [[package]]
 name = "scoped_threadpool"
 version = "0.1.9"
@@ -454,6 +484,12 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
+[[package]]
+name = "serde"
+version = "1.0.147"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d193d69bae983fc11a79df82342761dfbf28a99fc8d203dca4c3c1b590948965"
+
 [[package]]
 name = "smallvec"
 version = "1.10.0"