Fix typos and tweak documentation
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	src/p4est_mesh.h
Tweak documentation
Fix MPI warning in lnodes
Replace some P4EST_MPI with P4EST_ENABLE_MPI
Run s/P4EST_DEBUG/P4EST_ENABLE_DEBUG/
Some search and replace in test
Some search and replace in examples
mark error on website
Update libsc for config fixes
Tweak web page
Merge minor web page update