PPI doesn't detect `s` with alphanumeric delimiter

[happy-barney]

Example:

$foo =~ s (a) bob

Happen only when first Section uses paired delimiters and second section changes to letters.
Non-alphanumeric or digits characters works.

Proposal:

• introduce new Section token, quotelike keywords with two sections will put "expect section" twice on stack, so Parser can act accordingly.
• Section will have methods accessing delimiter, content, and "padding" (whitespaces before Section)

[happy-barney]

It will be nice to bless section hashes so one can do more operations, eg: access / modify gap before section (whitespaces around parentheses in my example).

Maybe even introduce concept of "children of token". Such concept will allow to model every element of quotelike using dedicated classes, as well as add support for interpolated code.