Ref issue #98 Change the docstring of the sandbox/gas/obrf/go script.
Ref issue #98 Add solvcon.parcel.gas.oblique_shock for calculation of oblique shock wave relations.

Based on *Modern Compressible Flow: With Historical Perspective* 3/e by J. D. Anderson, organize the relevant oblique shock wave relations that can be used for calculating the flow properties in all the three zones of the problem of oblique shock reflection from wall.

Full description of the reflection problem and the formulation is yet to be added.
Ref issue #98 Write document plan for the example problem of oblique shock reflection.
Ref issue #98 Use rounded value for doc tests in solvcon.parcel.gas.oblique_shock.
Ref issue #98 Edit documents for oblique shock reflection.
Ref issue #98 Add a schemetic of a single oblique shock wave resulted from a wedge.
Ref issue #98 Add a schematic of the reflection of oblique shock wave from a wall
Ref issue #98 add a schematic to assist the derivation of the relations across the oblique shock
Ref issue #98 remove obsolete code.
Ref issue #98 finish sandbox/gas/obrf and move it to examples/gas/obrf, and create examples/gas/run_gas_obrf.sh.

--HG--
rename : sandbox/gas/obrf/go => examples/gas/obrf/go
rename : sandbox/gas/obrf/obrf.tmpl => examples/gas/obrf/obrf.tmpl
Merged in yungyuc/scdev (pull request #45)

Finish examples/gas/obrf.