Expose a programmatic API

[perrin4869]

We are using this module in https://github.com/agentk/fontfacegen, but unfortunately, without a programmatic API, it is a bit hard to integrate. I think it should be a simple matter of adding a main field to package.json, as follows:

{
...
main: 'index.js'
...
}

Helps solve dotcore64/fontfacegen#32

[puzrin]

Close as declined - path should be resolved properly at your side.