Add linksInNewTab config option

[ocdtrekkie]

All credit due to @drmuey, reference is #659 for his work. This should merge against the current codebase.

[joshbruce]

Why not post the Issue instead of a PR as was suggested?

This still doesn't comply with the specs.
Still doesn't have tests.
And doesn't fit with the focus of the community right now.

Flagged for 0.5.0 at the moment.

[ocdtrekkie]

You wanted a big green button. I am looking at how to add a test and will add it to this branch.

[joshbruce]

Taking 'em one at a time. I appreciate the zeal. Let's see where it goes. :)

[joshbruce]

I should note, we haven't fully fleshed out the extensibility approach; so, not sure how much will change by the time we actually get to this...or if we will, to be honest. The more Marked takes on, the more chance there is for Marked to be in error...none of us are paid to maintain the code; so, it is in all of our best interests to keep it small - see #964

[ocdtrekkie]

I wrangled the testing setup a bit, the Linux VM I had handy is... outdated. I got an NPM error before and after adding my test, but after tweaking it a bit (I missed adding the <p> tags originally), it shows as completed.

[ocdtrekkie]

I completely understand the desire for brevity. I believe this PR is very brief, and it touches an extremely small amount of code. I believe the likelihood of this PR leading to bugs is small. The only thing I can think of that someone will need to be aware of, is that if code is added to add any other properties to the <a> structure, they will need to have a leading space, as this code does (and the title tag also does), before the new property. It should coexist with any new properties added similarly to itself.

[styfle]

I think you would want to add a few additional attributes to avoid cross-origin vulnerabilities such as rel=noopener. Also what about rel=nofollow? It's hard to know what the user wants in this scenario.

[ocdtrekkie]

@styfle The original PR for this feature was created in 2015. I have pretty much abandoned all hope for marked at this point.

[UziTech]

I think this feature would be better as an extension. it shouldn't be too hard to provide a renderer that does this.

[styfle]

@UziTech Agreed, there are too many variables here that it doesn't make sense to be in core.