feat: implement in memory store

1. the store works as a temporary store for connection data such as chats, messages & contacts
2. the store is primarily meant to illustrate the usage of the event emitter as a way to construct the state of the connection. This will likely be very inefficient to perform well at scale
3. the store is meant to be a quick way to have some visibility of data while testing
4. the store works for both legacy & MD connections

package.json

@@ -48,7 +48,8 @@
   "peerDependencies": {
     "jimp": "^0.16.1",
     "qrcode-terminal": "^0.12.0",
-    "sharp": "^0.29.3"
+    "sharp": "^0.29.3",
+    "@adiwajshing/keyed-db": "^0.2.4"
   },
   "files": [
     "lib/*",
@@ -58,6 +59,7 @@
   ],
   "devDependencies": {
     "@adiwajshing/eslint-config": "git+https://github.com/adiwajshing/eslint-config",
+    "@adiwajshing/keyed-db": "^0.2.4",
     "@types/got": "^9.6.11",
     "@types/jest": "^26.0.24",
     "@types/node": "^14.6.2",