big huge changes, so i dont remember everything.

* renaming, e.g. LU ---> FullPivLU
* split tests framework: more robust, e.g. dont generate empty tests if a number is skipped
* make all remaining tests use that splitting, as needed.
* Fix 4x4 inversion (see stable branch)
* Transform::inverse() and geo_transform test : adapt to new inverse() API, it was also trying to instantiate inverse() for 3x4 matrices.
* CMakeLists: more robust regexp to parse the version number
* misc fixes in unit tests

doc/snippets/Tutorial_solve_reuse_decomposition.cpp

@@ -1,6 +1,6 @@
 Matrix3f A(3,3);
 A << 1,2,3,  4,5,6,  7,8,10;
-PartialLU<Matrix3f> luOfA(A); // compute LU decomposition of A
+PartialPivLU<Matrix3f> luOfA(A); // compute LU decomposition of A
 Vector3f b;
 b << 3,3,4;
 Vector3f x;