use `npm run` for build

use `npm run` to build and reduce devDependencies as much as possible to gain dedupe-friendly dependency chain.

TODO
----------
- [x] Reduce to minimal devDependencies
- [x] Remove gulpfile
- [x] Travis settings
- [x] Extract espower-cli out -> done. [espower-cli](https://github.com/twada/espower-cli)
- [x] Extract dereserve out -> done. [dereserve](https://github.com/twada/dereserve)
- [x] README