parse a format (see perldoc -f format) as a single token.

[reneeb]

Currently PPI parses formats in a wrong way (see also Perl-Critic/Perl-Critic#917)

Without this fix, this code:

format BYDEPTH_TOP =
Top disk utilization in @*, @* level(s) deep
                        $BASEPATH, $DEPTH
================================================================================

subpath                                                         disk utilization
-------                                                         ----------------
.

sub print_anything {
}

is parsed as

PPI::Document
  PPI::Statement
    PPI::Token::Word  	'format'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'BYDEPTH_TOP'
    PPI::Token::Whitespace  	' '
    PPI::Token::Operator  	'='
    PPI::Token::Whitespace  	'\n'
    PPI::Token::Word  	'Top'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'disk'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'utilization'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'in'
    PPI::Token::Whitespace  	' '
    PPI::Token::Magic  	'@*'
    PPI::Token::Operator  	','
    PPI::Token::Whitespace  	' '
    PPI::Token::Magic  	'@*'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'level'
    PPI::Structure::List  	( ... ???
      PPI::Statement::Expression
        PPI::Token::Regexp::Substitute  	's) deep\n                        $BASEPATH, $DEPTH\n================================================================================\n\nsubpath                                                         disk utilization\n-------                                                         ----------------\n.\n\nsub print_anything {\n}\n'

This completely wrong... With this fix, this is parsed as

PPI::Document
  PPI::Token::Format  	'format BYDEPTH_TOP =\nTop disk utilization in @*, @* level(s) deep\n                        $BASEPATH, $DEPTH\n================================================================================\n\nsubpath                                                         disk utilization\n-------                                                         ----------------\n.\n'
  PPI::Token::Whitespace  	'\n'
  PPI::Statement::Sub
    PPI::Token::Word  	'sub'
    PPI::Token::Whitespace  	' '
    PPI::Token::Word  	'print_anything'
    PPI::Token::Whitespace  	' '
    PPI::Structure::Block  	{ ... }
      PPI::Token::Whitespace  	'\n'
  PPI::Token::Whitespace  	'\n'

[oalders]

Closing and re-opening to trigger CI.

[oalders]

@wchristian did you have any thoughts on this one?