libpkgconf: fragment: rework quoting and lexing (closes #139, #153) we now use POSIX-style quoting for all fragments. it is our belief that this is the most optimal behaviour for portability, because all POSIX-compliant tools require single-quotes to be considered as literal (closes #153). because of this, we are able to remove some hacks on the lexer side which were there to simulate pkg-config quoting, but were basically utterly wrong (closes #139).