Add default logmanager

[Jark]

As discussed in #111, this will add a default log manager which will log to the debug console to make it so that we can detect errors in setup and operation easier.

[tomkuijsten]

Looks good, but one small question. Will it ever work? You are using Debug.WriteLine which will be removed during optimization in Release mode. Our nuget package contains only Release mode assemblies. It will work for us, during development of Restup itself, it won't work for consumers of the package.

[tomkuijsten]

Should this check be moved to the Debug method itself. Pretty error prone if you have to check this yourself everytime.

[Jark]

The debug method itself should have it as well, the only thing the _log.IsDebugEnabled() checks will make sure that the string won't be computed. Since these are in the critical path for request handling I didn't want the strings to be computed.

[tomkuijsten]

Is this something we should still look at?

[Jark]

I'll take a look at this at some point, but probably not to soon. Might have some time this weekend.