Emit only updated files during incremental compilation

[kimamula]

TypeScript does not emit unchanged files when using watch option.

• Change only updated files when using watch option. microsoft/TypeScript#3113
• Avoid writing files that are not changed while compiling incrementally. microsoft/TypeScript#6937

It is likely that this feature is not available in gulp-typescript, as it does not support watch option.
It would be nice if gulp-typescript mimic this feature during incremental compilation.

[kimamula]

I noticed that this would be quite difficult because

• gulp-typescript does not know dest location
• Output of gulp-typescript may be further processed

Sorry.

[kkovalevskiy]

@kimamula I suppose that it would be nice have such option in gulp-typescript configuration, it can be pretty useful for incremental builds and we could skip emitting phase for unchanged files (it can take pretty much time if you have a big project with >3000 .ts files). So, it would be great if such option would exist and can be configurable outside of gulp-typescript.