handle cash-in errors

lib/error.js

@@ -1,11 +1,14 @@
-const E = function generateError (name) {
+const _ = require('lodash/fp')
+
+const E = function (name) {
   var CustomErr = function (msg) {
-    this.message = msg
+    this.message = msg || _.startCase(name)
     this.name = name
     Error.captureStackTrace(this, CustomErr)
   }
   CustomErr.prototype = Object.create(Error.prototype)
   CustomErr.prototype.constructor = CustomErr
+  CustomErr.code = name
 
   return CustomErr
 }
@@ -18,3 +21,4 @@ function register (errorName) {
 
 register('BadNumberError')
 register('NoDataError')
+register('InsufficientFundsError')