Throw exceptions instead of being silent, just like Scala

[mkurz]

This was bothering me a bit while reviewing

• Migrate to pure Java implementation #242

because even though Scala does not require you to catch checked exceptions, it does throw them at runtime if they occur.
I don't really like being silent and just swallowing the errors and continuing like nothing happened. If people get strange behaviour because some files can't be watched or whatever it's very hard to figure out what's going on, so IMHO better to just fail with an exception. Given that the equivalent Scala code did the same, I guess this exceptions will not really occur in real life anyway.

Also, look at that better-files says about the walk method:

• https://github.com/pathikrit/better-files/blob/v3.9.2/core/src/main/scala/better/files/File.scala#L743

    Files.walk(path, maxDepth, visitOptions: _*) // TODO: that ignores I/O errors?

So the devs were not even sure what's happening (this line was added 8+ years ago to be fair). What happens is at Runtime the IOException will be thrown. What they did now is:
pathikrit/better-files@0a22873#diff-1eed0c8cd6c94c548b033043e1669d94cb999fd88dc17d9bc3db3f6247fb51e2L689
move that in and GitHub issue pathikrit/better-files#590 so they figure out what to do.
Anyway, I think throwing is better now. Actually nothing changes from previous play-file-watch versions...