N220: Improve the C++ template. (#227)
N220: Improve the C++ template. (#227)

* Use macros to avoid repetition.
* Use whitespace suppression to improve the formatting of the template.
FFIG/ffig,jbcoe/C_API_generation,FFIG/ffig,FFIG/ffig,FFIG/ffig,FFIG/ffig,jbcoe/C_API_generation,FFIG/ffig,jbcoe/C_API_generation,FFIG/ffig,FFIG/ffig,jbcoe/C_API_generation