We should consider replacing pubspec dependency with something else

[mateusfccp]

We currently depend on pubspec. Unfortunately, pubspec is abandoned, with some issues and pull requests that were never reviewed or merged.

Recently, #658 raised up the question if we should replace pubspec with something else, considering the current scenario of pubspec.

As replacing the dependency would result in considerable changes, as we would have to deal with a new API, I decided to open this topic so we can discuss what is the best solution for this.

One possible replacement could be pubspec_manager.