Put vectors, matrix and aabb in namespace virvo
operator* for multiplying matrices with vectors
Put clamp() in namespace virvo::toolshed
Utility functions for Vec3 in namespace virvo

dot(), length(), normalize() etc.
Having these in a namespace makes it easier to switch to
an alternative implementation
get{ModelView|Projection}Matrix return values

In addition to the ones modifying a reference parameter
virvo::Matrix::getRow() must be const
SSE-optimized version of softrayrend
Ray renderers are virvo plugins

* All virvo plugins AND all DeskVOX plugins are located in VV_PLUGIN_PATH
* Introducing renderer factory option arch ["best"|"cuda"|"fpu"|"sse"|"sse4_1"]
  for ray renderer plugins
* works in vview and vox-desk-qt
* TODO: close() rayrend plugins