Package in nixpkgs

[l0b0]

Just creating this to let you know I'm going to try to package this for nixpkgs. We'll see if I get anywhere; I've never used Dart, I don't know any of the toolchain, and it looks like dart2native isn't packaged in nixpkgs dart2native is now dart compile exe.

In terms of packaging for distros in general, if you have time it would be great if you could do the following:

• Add tags to milestone commits to give packagers something to call a version other than YYYY-MM-DD or whatever the packager settles on.
• Version control pubspec.lock (as recommended for applications) to improve the chances that you and packagers are going to get the same results when building.

Please let me know if you want more info about why and how. Oh, and thank you so much for this cool tool!

The package is ready for review. Please let me know if there's anything you'd want me to change about it, either before or after it's merged. Otherwise please feel free to close this.