Add an errror warning if project file (.json or .conf) is not found o…

…r corrupted.

Support of JSON format at configuration file.

Incorporation mesh file name into configuration file.

Update README.md

Change of sources data structure

Add user defined source function in conf file: implementation of math function parser
Use of VTK native binary output file routines in place of xml text output

speed up improvement

Using gmsh 4.10.5

New minor update

Update Mesh.cpp

Fix indentation 2

travis compatibility fix