Replace autotools with CMake

[fmang]

Pros:

• (Important) It is cross-platform, in particular it targets Windows Windows support #38.
• It is relatively modern.
• It integrates with many IDE (meh).
• The build objects are isolated in a separate directory, not directly into the source tree.
• It is less scary than M4 macros?

Cons:

• POSIX users are less used to it. No more ./configure --prefix=$HOME/.local CXXFLAGS=-O3 but cmake -DWHAT_WAS_IT_AGAIN?.
• It is an extra dependency at build-time. (who cares?)

In both cases, writing build scripts is a painful experience. Reading the pros/cons back, most matters sound trivial; the one decisive point is cross-platform support.

Many other fancy tools exist, but I'd rather use a solid one everybody knows.

I plan to toy with CMake by next week, and remain open for advice.

[fmang]

Okay, let's do this.

[fmang]

Done!

It was easier than expected, except for #60.