build: allow symfony 7.0

build: min php version is 8.0.2

fix: extinf attributes should be escaped by double quotes (") only.

#26

fix: better compatibility with https://datatracker.ietf.org/doc/html/…

…rfc8216#section-4.3.2.1

#25

fix: parse escaped quotes

#24

build: drop php 7.1 and 7.2 support

upd appveyor

drop php 5.6/7.0 support

use type hinting, micro-optimizations

fix readme

minor refactoring