Unused fields in config file should print warnings

[wscott]

Right now the toml file is used for setting but any extra unused settings are just ignored and most everything has a default value.

So if you make a typo in your file that value will just be ignored and it might not be obvious.

A nice feature would be to print a warning about any data items in the user's toml file that are not used. One way to do this would be to delete each key as it is used and then print warnings about anything remaining. Also include warnings about any keys that have the wrong type.

[wscott]

I have a PR with a version of this: #30