Add package.json

[dmitryt]

It will be more convenient to install the library via npm

[Grawl]

there's a fork with package.json https://github.com/dbeerten/input-masking

now we have to publish it on NPM registry

[stephencweiss]

For what it's worth, I went ahead and published -- https://github.com/estelle/input-masking/pull/19