added default target all to Makefile.common that does 'make .plots' and 'make .htmls'
Removed obsolete regression scripts and added a new regression_tests.py
added make_all.py script to do 'make all' in all subdirectories, e.g. of an examples directory.  Adapted from clawpack/doc/doc/gallery/make_plots.py and should be used instead for producing galleries.
improved make_all and regression_tests
Merge pull request #71 from rjleveque/make_all

add 'make all' default
Added missing conversion script
Merge pull request #72 from rjleveque/convert43to46

Added missing conversion script