Add support for multi-line regexs to ronin grep and ronin extract

[postmodern]

Support for matching multi-line regexps to the ronin grep and ronin extract commands. Currently multi-line regexps such as the --ssh-private-key option do not work properly.

[postmodern]

Options such as --ssh-private-key, defined in Ronin::CLI::PatternOptions (lib/ronin/cli/pattern_options.rb), should implicitly enable the multi-line mode. Then the process_input methods of the Grep and Extract commands should switch to reading the entire file, instead of processing each line.

[postmodern]

We could also automatically check if the regexp is multi-line and enable multi-line mode:

lib/ronin/cli/pattern_options.rb:

def multiline?
  (@pattern.options & Regexp::MULTILINE) > 0
end

lib/ronin/cli/commands/grep.rb:

def process_input(input)
  if multiline?
    ...
  else
    ...
  end
end