Create 3.6.max_pages.py

# The web crawler we built at the end of Unit 3 has some serious
# flaws if we were going to use it in a real crawler. One
# problem is if we start with a good seed page, it might
# run for an extremely long time (even forever, since the
# number of URLS on the web is not actually finite). The final two
# questions of the homework ask you to explore two different ways
# to limit the pages that it can crawl.

# Modify the crawl_web procedure to take a second parameter,
# max_pages, that limits the number of pages to crawl.
# Your procedure should terminate the crawl after
# max_pages different pages have been crawled, or when
# there are no more pages to crawl.

# The following definition of get_page provides an interface
# to the website found at http://www.udacity.com/cs101x/index.html

# The function output order does not affect grading.