Allow overridden parameter types on GET/DELETE

[jasperblues]

I'm not sure if this will be useful to others (hopefully, as it will alleviate our need to sync with upstream) however I needed to add support for DELETE with a JSON request body. (API didn't strictly adhere to spec).

For uniformity, provided also for GET. (In the past I have seen GET reqs with url encoded params along with a serialized body - this would not be supported).

[jasperblues]

@3lvis After the above PR, have another, which is the introduction of an ErrorLogger:

import Foundation

public protocol ErrorLogger {

    func log(_ message: String)

    func flush()

}

class ConsoleErrorLogger : ErrorLogger {

    func log(_ message: String) {
        print(message)
    }

    func flush() {} // Not required for console 

}

Default (provided) implementation logs to console, just as currently, custom version can, for example, log to Sentry.

[mkll]

@jasperblues It seems to me that the name chosen is not entirely successful. We can log not only errors, but any messages in general, right?

Maybe a name like Logger would be more appropriate?

[mkll]

After all, the name ErrorHandler implies an error handler, not simple message logging. I mean error trapping, recovery, etc.

[jasperblues]

Ah yes @mkll you're right, that was a terrible choice! ErrorLogger would be better. (This only intercepts the logging that occurs on error, rest of the console logging is left alone).

[jasperblues]

(More complicated, but better) A LogProvider that emits a (non-shared) instance of ErrorLogger will to prevent two errors being logged at the same time from entangling.