Add .solhint.json configuration file

Author: tipspay-dev

.solhint.json

@@ -0,0 +1,9 @@
+{
+  "extends": "solhint:recommended",
+  "rules": {
+    "max-line-length": ["warn", 120],
+    "func-visibility": ["error", { "ignoreConstructors": true }],
+    "no-unused-vars": "warn",
+    "quotes": ["error", "double"]
+  }
+}