Implements --sitemaps. Closes chfoo/wpull#69.
url.py: Preseves whether query strings contain '='.

Closes chfoo/wpull#76
scraper.SitemapScraper: Catches XML parse errors.
Merge branch 'issue/69-sitemaps' into develop

Conflicts:
	wpull/scraper.py
changelog.rst,terse_options.rst: Update for --sitemaps option.
scraper.py: Renames urljoin to urljoin_safe and return None.
url.py: Makes URLInfo.url a property.

Removes redundant URLInfo.normalize. Adds url.normalize() convenience
function.
Merge branch 'issue/76-query-string-delim' into develop

Conflicts:
	doc/changelog.rst