Add ability to manually save screenshots with custom prefixes

[mtancoigne]

I like to make custom screenshots for demonstration purpose, so this PR updates screenshot_and_save_page and screenshot_and_open_image with two additional parameters: prefix and html

This is useful to differentiate screenshots from failures.

[mattheworiordan]

I appreciate the contribution, but please see my comments in regards to changes I would require to merge this I am afraid. Shout if you want to discuss any of this.

[mattheworiordan]

I am afraid I cannot approve this. I am happy to support this PR, however we need to see;

• Use of options in this method so that adding new options in future is more easily supported, and the code is more readable. For example, I'd expect to see screenshot_and_save_page(prefix: 'custom_prefix', html: true).
• I am not sure even the former arg html makes sense. What does that even mean, given your comment says "image only" and the default is true?
• I'd like to see this approach with argument options = {} carried through internal methods
• We need to have some tests for this, even if very basic, so that changes in future won't introduce regressions.

[mtancoigne]

No problem, I'll try to fix this this week.

[mtancoigne]

Hi !

For the arguments, do you prefer options or keyword arguments ?

For html, this was a mistake on my side in the README, it should have been false. I set this option so one can save only image screenshots without breaking the way the library works today.

[mattheworiordan]

For the arguments, do you prefer options or keyword arguments ?

Well options because we still support older versions of Ruby, for now.

[mtancoigne]

Hi! I think i'm ready with the changes.