(experimental) Support grunt-contrib-watch style files: srcArray

[jpommerening]

I'm not sure if this breaks some tasks, but couldn't Grunt support the grunt-contrib-watch style of specifying files? When I started using Grunt I found it pretty confusing to have this one "blessed" watch plugin that is used everywhere but that is configured differently from every other plugin.

Do you think the benefits outweigh the downside of having to support yet another way of specifying files? (TBH it's just treating files like src in case files contains strings)

Ex: increasing levels of detail/verbosity in target.files

// new / grunt-contrib-watch style
target1: {
  files: ['**/*.js']
},
// files object
target2: {
  files: { 'dist/file.js': ['**/*.js'] }
},
// files objects in array
target3: {
  files: [
    { 'dist/file-a.js': ['a/**/*.js'] },
    { 'dist/file-b.js': ['b/**/*.js'] }
  ]
},
// files array
target4: {
  files: [
    { src: 'dist/file-a.js', dest: ['a/**/*.js'], /* ... */ },
    { src: 'dist/file-b.js', dest: ['b/**/*.js'], /* ... */ }
  ]
}

[shama]

I believe the rest of the Grunt team was agreeing they wanted less src/dest block style types as its a good source of confusion so I don't think we should add another. If anything, we should just make it more clear the watch task is not a multi task like the other tasks and behaves differently because it operates differently than any other task. But that is the primary reason grunt-contrib-watch's style is different.

Thanks for the PR though! Much appreciated!