NPM packaging: Missing package.json

[MaybeJustJames]

Hi @cmzmasek ,
I would like to use phyloxml in the ongoing development of the phyD3 phylogenetic tree visualiser. As far as I understand you need to have a package.json file to publish to NPM but I don't see one? That package.json file should contain the sax dependency rather than requiring users to manually vendor sax.js into their own projects.
Would you accept a PR adding a package.json?