Proper naming of attributes

[ichux]

@miyakogi

I want to send a pull request, but, can I do some renaming of attributes as advised here: http://legacy.python.org/dev/peps/pep-0008/#prescriptive-naming-conventions e.g.

self._ignoreHTTPSErrors becomes self._ignore_https_errors

[miyakogi]

Pyppeteer is using same attribute names to puppeteer, in order to make it easy to find changes and to port code from puppeteer (JS) to pyppeteer (python).

Thank you for considering to send PR.