custom integrators for II order systems : Euler explicit II order, Euler semi-implicit
New explicit integrator, Heun (like Runge Kutta explicit, 2nd)
The ChIntegrable and ChIntegrableIIorder classes now define interface functions for (future) implicit integrators.
Also, the II order class has fallback functions so that it can be used also with all I order integrators.
Improved demos
Fix issue with GCC compiler
Added Leapfrog explicit integrator.
To be checked because it should be symplectic, but looks like it is not..
Added Euler Implicit integrator, with Newton Raphson iterations etc.
It works ok.
Added trapezoidal implicit integrator, with NR iterations and 2nd order accuracy.
Tested. It works ok.
Added prototype of HHT implicit integrator.
NOTE: not working, it must be tested.
Better comments to code.
Various changes to the ChIntegrable classes
Updated tests about the ChTimestepper stuff
Fixed the Leapfrog integrator
Changed several data structures associated with rigid contact to use double precision, including C_q, E_q, contact normal, contact plane, friction, cohesion, etc. Updated the APGD iterative solver to match Heyn's PhD thesis.
Fixed an error in setting the format for the 'b' vector.
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop