GSOC 2017 [Algorithm improvements to KD-Tree module: applications to ICP]

[pranjal-rai]

No description provided.

[jlblancoc]

I still have to review and see how to solve all conflicts.

In the meanwhile, I have some preliminary changes that you could add to your repo (and they'll be automatically appended to this PR):

• Please, update the main README.md, and add your name to the field author of the Bibtex citation.
• Update the section "Code examples" with the new ones. Specially, the one for dynamic-size datasets.
• Update the sections "what can /can't nanoflann do". I'll refine them later, just add what you changed in your own words. For example, I'd still like to add the possibility mixing different metrics via a std::tuple so it could be mentioned as "future works", but I can add those comments, I don't mind.