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Data structure:
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elem: Three vertices forming a triangle. Given in counter-clockwise order

edge: two vertices forming an edge. For a boundary edge, when we go from
vertex one to vertex two, the computational domain lies to the left of the
edge

tedge: Triangles adjacent to an edge; left is first and then right.

esue: Elements surrounding an element. Required only for implicit scheme

vedge: The vertices opposite to an edge; left first then right. Used for
reconstruction.

spts: Solid wall points

bdedge: For each solid wall point, the two boundary edges sharing that point.
Used for calculating wall normal, which is required for inviscid bc.

esubp: Elements surrounding a boundary point. Required for vertex averaging.

ptype: Type of vertex.


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Files
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flo: 
   output: FLO.DAT

adj: 
   input : FLO.DAT 
   output: ADJ.DAT, ADJ.DXY

adjoint: 
   input : ADJ.DXY (gradient wrt coordinates)
   output: DEF.OUT (gradient wrt boundary coordinates)

shape:
   input : DEF.OUT
   output: gradient wrt shape parameters, maybe HicksHenne

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Changelog
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Following functions have been changed
   solid_flux
   farfield_flux
   clcd
   costfunc

Linear interpolation has been replaced with first order treatment. This would
be more robust while results dont seem to be affected.

* Added entropy fix for |u| eigenvalues in roe flux