Update to latest SMAPI & refactor

[Pathoschild]

This pull request...

• migrates to the latest SMAPI APIs (which lets us simplify the config and logging code quite a bit);
• marks all internal classes internal;
• copyedits & adds missing code documentation;
• applies .NET best practices (e.g. one class per file);
• applies SMAPI best practices (e.g. avoid lambdas as event handlers);
• removes now-unused dependencies on Json.NET and the MSBuild extensions pack.

[alexb5dh]

Big thanks for refactoring and documentation.
Will check this in game and publish a new release in a few days.

[alexb5dh]

Looks like Json.NET reference removal was too early since Keys serialization as string will only be added in 1.9.

[Pathoschild]

The previous version works fine with SMAPI 1.8; how about releasing this as the SMAPI 1.9 / Stardew Valley 1.2 version?

[alexb5dh]

I'm all for it. Are there any estimation dates for 1.2?

[Pathoschild]

Not that I know of, but development and feedback is slowing down so I'd guess within the next week or two.

[alexb5dh]

Ok, I'll keep track of the news then.