Version 3.3.4 is the latest stable release.

Signed-off-by: Anders Martinsson <anders.martinsson@intinor.se>

Rewrote cmake, now a bit cleaner, checks for compiler flags.

Added Eigen3, v3.2.8 in case it's not found on the system.

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>