find ranges of page numbers

[tangledhelix]

Ports a feature from PPtools: find page numbers in various formats and display them (roman first, arabic next).

Understands different formats like Page_1, page_1, page1 (in id attribute). Also attempts to parse numbers from <span class="pagenum"> tags (p. 1, [Pg 1], etc.).

Example of what this looked like in PPTools:

Example from this change:

----- document info ------------------------------------------------------------
[info] page numbers ( roman): i–xi
[info] page numbers (arabic): 13–168

Can display multiple ranges if numbers are missing from the sequence:

----- document info ------------------------------------------------------------
[info] page numbers ( roman): i–iii, v–xi
[info] page numbers (arabic): 13–23, 25–45, 47–168

[tangledhelix]

Note that this adds to requirements.py, the roman module is required.

[cpeel]

Can we follow the convention of grouping the built-in packages together, a newline, and then the 3rd party?

import sys
import os
import argparse
import itertools
from time import strftime
from html.parser import HTMLParser

import regex as re  # for unicode support
import roman
from PIL import Image

Ideally each would be alpha-sorted but I'm not going to get wound around the axle about it.

[tangledhelix]

done! and sorted :)