Make invalid options supplied to the loader be reported as an error

[johnnyreilly]

At present invalid loader options are just ignored.

About once a week or so, someone will raise an issue against ts-loader about ts-loader not working. Further investigation often reveals this to be a configuration issue. Since this results in a fair amount of wasted time (and also that I suspect not everyone goes to the trouble of raising an issue here) I'm planning to make ts-loader throw an error when invalid options are supplied.

Fail fast and fix it is the aim of the game.

If anyone knows of any reason why this could be problematic to them then do speak up - otherwise this is likely to ship in the next release of ts-loader.

Although this is strictly speaking a "breaking changes" change I'm probably not going to increment the version just for this. My reasoning is: anyone who is broken by this already has a broken config and will likely be grateful for the new information. Again, if anyone has other views on this I'm open to hearing them.

Thanks!

[johnnyreilly]

See #630