Remove dependency on file-system

[ArsalanDotMe]

A useful way to use this package would be to provide the input file as buffer so that we could maybe get the file from a database and pass it to your package to get an html string as output. The dependency on file system should not be enforced.

[haydenbleasel]

+1, returning a string or buffer would be optimal.

[iapain]

👍 Pull request most welcome.

[maczor]

+1