Replaced AsciiDoc headings with new style

[mbrukman]

Fixes #17.

As described in the Asciidoc best practices document:
http://asciidoctor.org/docs/asciidoc-recommended-practices/#section-titles
using heading markers using underlines of various characters is not recommended
for several reasons:

• hard to remember which character means which level header
• hard to maintain the correct number of characters (must match heading line)

This change takes the same approach as a similar change in JanusGraph:
JanusGraph/janusgraph@dc67ce7
with some minor modifications to handle Windows-style EOL \r\n in this file,
whereas the other change works only with UNIX-style EOL \n.

What that required was stripping just the Windows-style EOL characters before doing
the regex matches:

line = line.rstrip('\r\n')

Note that using line = line.rstrip() doesn't work here, because some lines
already end with a whitespace character, which leads to spurious diffs.

Then, we manually added them back via:

sys.stdout.write('%s\r\n' % ...)

Using print in this case would give us UNIX-style EOL, causing the entire file
to show a diff on every line.

Here's the entire file with modifications for this run, which may be useful in
the future if/when someone needs to reapply this to an AsciiDoc file formatted
with Windows EOL chars:

#!/usr/bin/python

import re
import sys

def main(argv):
    # http://asciidoctor.org/docs/asciidoc-recommended-practices/#section-titles
    patterns = [
        (re.compile('^=+$'), '='),
        (re.compile('^-+$'), '=='),
        (re.compile('^~+$'), '==='),
        (re.compile('^\^+$'), '===='),
        (re.compile('^\++$'), '====='),
    ]

    with open(argv[1], 'r') as input_file:
        prev_line = None
        curr_line = None
        for line in input_file.readlines():
            line = line.rstrip('\r\n')
            prev_line = curr_line
            curr_line = line

            if prev_line is None:
                continue

            for pattern, heading in patterns:
                if pattern.match(curr_line) and len(prev_line) == len(curr_line):
                    sys.stdout.write('%s %s\r\n' % (heading, prev_line))
                    prev_line = None
                    curr_line = None
                    break

            if prev_line is not None:
                sys.stdout.write('%s\r\n' % prev_line)

        # end for
        if curr_line is not None:
            sys.stdout.write(curr_line)

    # end with

if __name__ == '__main__':
    main(sys.argv)

[krlawrence]

We just started work on a Second Edition of Practical Gremlin. As part of that we will update the entire tool chain and factor in these types of changes. I'm leaving this PR open as a reminder.