Support reading from buffer & other improvements

[Roba1993]

Hi @anvie,

I like your library and the simplicity to extract data from multiple files without much dependencies. With this PR I add support to read the file from the buffer. In addition I created a function to read any generic file, which makes it a lot easier to use. Furthermore I included an enum to provide the type information in a more structured way.

I hope you can accept my changes.

Thanks, Robert