* Split core lib into multiple files
* Refactor data encoding methods
* Refactor data masking process
* Improve qr code generation process
* Increase minimum required node version to 0.10
* Add linter
* Add tests and tests coverage
* Update travis config to fix compilation issues
* Add examples folder
* Add missing license tag in package.json
* Update build script and add sourcemap support
* Publish only strictly needed files on npm
* Update readme
When build node-qrcode, it need `libgif-dev`. But the doc doesn't mention it.
Change:
```
sudo apt-get install libpixman-1-dev libcairo2-dev libpangocairo-1.0-0 libpango1.0-dev
```
To:
```
sudo apt-get install libpixman-1-dev libcairo2-dev libpangocairo-1.0-0 libpango1.0-dev libgif-dev
```
