feat: rewrite wasm exports api

[axetroy]

fixed: #37

remove old exported functons print_document and run and others callback.

just take one function generate_pdf_bytes and it returns bytes directly.

NOTE:

Compilation and examples have been tested in my environment

/cc @jussiniinikoski

[jussiniinikoski]

I am going to archive this repo, so please use your fork for whatever you need.