Debug

Find that when evaluating transcendental functions on gpu directly (blas1::transform, blas1::evaluate) we get yet another result. Second, json.h is no longer included by geometries.h in order to fix compilation errors when README is followed to the letter. Third, began to fix the multiple translation unit problem (if algorithm.h is included by multiple translation units we get serious linker errors, which contradicts the claim that we are header only)

1. add exp test to evaluation_t that explicitly tests evaluation on gpu
2. include json.h manually by asela, feltor, feltor2D, asela2D, heat and polar, all geometries files and feltordiag, filamentdiag, and ncdiag
3. added static keyword to exblas functions and remove including vcl/instrset_detect.cpp, added a value_type to some average templates
4. added more info about json and netcdf installation in README
5. minor corrections in docu