syntax change: "foo +% bar" -> "foo+ % bar" (P6)

The separator syntax was made slightly more Perl6-ish.
Now all quantifiers must follow the repeated rule directly,
no whitespace allowed.
syntax change: proper separation operator "%!"
Markdown style improvements
more MD reformatting, reformulations

E.g. "The issues with the SLIF" -> "My issues"
bugfix: allow repetition without separator
add JSON parser example