Added 4 examples based on things in the tests directory

Cleaned up several examples that were in the tests/ directory and moved to examples/
Eventually they should be removed from tests/

Someone should check that these all work.

(Except that examples/acoustics_2d_radial/1drad for the scatter plot comparison won't work until classic 1d is available)

Note: examples/advection_2d_annuls won't plot properly without PR clawpack/visclaw#63 
where a new argument has been added to gaugetools.plot_gauge_locations