v2.0.x: support options in body parser
v2.0.x: make Loader.download protected
v2.0.x: support limit and length Loader options
v2.0.x: refactor Multipart options passing
v2.0.x: add types to bpdy parsers results
v2.0.x: support limit and length multipart parser options
v2.0.x: refactor tests
v2.0.x: cover Multipart with tests