Improve exclusion of files in minimatch

[marcooliveira]

Excluding files from a minimatch expression can be tricky, and the syntax can become a nightmare to read. Maybe we should come up with a simpler syntax?

If we take the cp example, we could support something like this:

files: {
  'src/**/*.js,!*.min.js': 'dst'
}

This would copy all the .js files, except those that end with .min.js, the exclamation mark being a negation (exclusion) operator, and the comma separating these. This expression could be composed of several comma separated expressions and, in order for a file to match, it would have to match ALL the expressions.

These sort of features should be provided in something like ctx.file, so that task creators don't have to do this by hand repetitively, and also it should be part of the automaton-lib. Check #45 for more information on this.

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[marcooliveira]

Check https://github.com/mklabs/node-fileset for ideas.

[marcooliveira]

Big breakthrough for this issue in #50 (comment). This will be the base for improving exclusions.