use cargo generate for templating

[drmason13]

Cargo generate is a cargo subcommand for templating new projects.

Integrating with it should only require a few changes to cargo.toml and then anyone who uses cargo-generate will be happy :) I'd like to make a pull request for these.

Example usage of cargo generate to use this quickstart:

cargo generate --git https://github.com/seed-rs/seed-quickstart --name my-new-seed-project