v1.2.0 release

code is now more meaningful
added available slices mechanism to use remaining []byte from the filtered parts
added MaxParseCount variable to limit parse loop
filter function now gets a []byte as a parameter
Storage removed
Marshaler removed
removed Header related things from parser.Parse function,
added Part struct to access data easily
added NewParser function,
Options renamed to ParserOptions,
Parse method removed from Options,
Options struct not implements Parser anymore, parser implements Parser interface now,
parser can be created with NewParser function,
now using Part struct instead of Header,
not using Parts struct anymore, now using Request struct.