Improve error handling

[mrodem]

In adapter.js, there is a _makeError function that creates instances of a custom Error class. According to the JSDoc, this function accepts two parameters; userMessage and description which should both be string. However, the description is sometimes given as a string and sometimes as an error object.

The custom Error class should ideally be named something other than Error. Then it can be instantiated directly without needing the intermediate _makeError function. Also, the use of the description parameter should be changed so that it is consistent.