Added examples/acoustics_2d_radial, copied from tests/acoustics-example1
added examples/euler_2d_quadrants, taken from tests/quadrants with some modifications
added examples/burgers_2d_square, copied from examples/burgers_pwconst with some modifications
added examples/acoustics_2d_radial/1drad, copied from examples/acoustics_2d_radial/1drad - NOT working...
Need to test after classic 1d codes have been added
added examples/advection_2d_annulus, copied from tests/annulus with some modifications
Merge pull request #57 from rjleveque/new_examples

Added 4 examples based on things in the tests directory