NPVI add-on for FEAP

*Latest version: v1.4 (14 July 2020)*

It is a common practice in the isogeometric analysis post-processing to use FE-like mesh formats to plot the results. In the first step, an FE-mesh corresponding to the IGA-mesh is created. After that simulation results such as displacements, stresses, principal stresses, etc. are projected onto the new mesh. The code to perform these actions is already included in the NURBFEAP/igaFEAP for the linear case. We have used the same approach and fitted the algorithms for our purposes. A similar routine to `uparaview.f` is used to write the output file.

The routine includes the following features:
- linear interpolation of the geometry and the solution field (using linear FE elements)
- quadratic interpolation of the geometry and the solution field (using quadratic FE elements)
- uniform and non-uniform subdivisions of the NURBS elements
- standard FEAP output of the IGA mesh (in form of Serendipity and Lagrangian finite elements)
- NEW post-processing of NURBS meshes using the so-called Bézier elements in Paraview (only for FEAP 8.5 and FEAP 8.6)
- NEW compress VTU files on-demand (currently by executing an external Python script)