New testing tool and fix broken links

[BorjaOuterelo]

Added a useful HTML testing tool.
First, run already pointed out broken links. Fix for those is also provided in this PR

[iluetkeb]

Excellent, been looking for sth like that. Note, however, that it does not seem to correctly check redirects. All of the links you corrected, except for tf2 one, actually work. I mean, the new versions are fine, but would not strictly have been necessary. Von meinem iPhone gesendet Am 28.02.2019 um 16:33 schrieb Borja Outerelo <notifications@github.com<mailto:notifications@github.com>>: @BorjaOuterelo<https://github.com/BorjaOuterelo> requested your review on: #10<https://github.com/microROS/microros.github.io/pull/10> New testing tool and fix broken links. — You are receiving this because your review was requested. Reply to this email directly, view it on GitHub<https://github.com/microROS/microros.github.io/pull/10#event-2171419924>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AARpguoLuA6YlnyKwRkf1Bncrdkib8eIks5vR_bFgaJpZM4bXFrk>.

[BorjaOuterelo]

I changed them because going through the links present in https://microros.github.io/docs/home/ I got 404 for all of them.
Going through the links present there work for you?
That may be an issue on my side. I am missing something?.

[iluetkeb]

These links really don't work, even though they worked when running Jekyll locally on my laptop. Apparently, something with the Jekyll-redirect plugin is wrong. We have to investigate that, because we put theses links into deliverables.
I've tested it now and https://microros.github.io/embedded_tf works, and redirects to .../docs/embedded_tf/. So, unclear why you got 404s!