Generator removing + replacing existing blocks in README and htaccess

Previously, running the generator against an existing genesis project would [add duplicate template blocks][duplicate-gist] to `README.md` and `.web/htaccess` without removing what was already there.

This PR should [instead replace said blocks][replacement-gist], and in addition add the current generator version from `bower.json`, for quick reference.

[duplicate-gist]: https://gist.github.com/EvanK/831fb6cc341ab80234a8
[replacement-gist]: https://gist.github.com/EvanK/66be3ed0f6b1a4df91cf