Remove magic `this` from tasks

Tasks will lose access to this during definition.

What used to be:

exports.default = function * (opts) {
  yield this.source(opts.src || 'src/**')...
}

Now looks like this:

exports.default = function * (fly, opts) {
  yield fly.source(opts.src || 'src/**')...
}

Note: The opts param is conditionally populated in both cases. This is already an implemented behavior.

Need Feedback

For 2.0, I think users should still have access to this but it will not be documented or encouraged.

Then in 3.0, the binding to this will be removed entirely.

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cc: @jbucaran @rauchg

[devmondo]

Awesome!!!

[rauchg]

This is fantastic