Fix noisy compiler warnings and add CMake support

[cschreib]

This PR goes a bit further than https://github.com/msokalski/delabella/pull/6, in fixing a couple more warnings. It also offers CMake support for easy inclusion into other projects.

[msokalski]

Looks ok, thanks. Last commit was a bit too heavy, most source diff tools wasn't able to sync properly, splitting it to smaller changes per commit would make reviewing way easier.

[msokalski]

Btw, may I ask what do you use dela for?

[cschreib]

Thanks for merging the PR! FYI on the last commit, unfortunately it was a bit of an "all or nothing" situation, where the main function had to be broken down into sub-sections to avoid shadowing. It is difficult to do that as a set of small changes. Here I did the bare minimum to remove shadowing, but for overall code clarity, it would probably be worth it to do a second pass and break it down further into logical units (removing duplicates as a separate function, etc.).

As for your last question. I am currently working on an unreleased video game. The game has a simulated galaxy with hundred to thousands of stars. I needed to connect stars with "wormholes" for travel, such that all stars are part of a single un-interrupted network (i.e., there is a path that connects any two stars). I also needed it to look "nice" :) I use your library to form the Delaunay triangulation of the stars' positions, then build a minimum spanning tree out of the output graph. Adding a few extra edges to the graph to add loops and more interesting paths, I end up with something like this:

[msokalski]

Nice, thanks.