N216: Improve C template by using jinja2 macros and whitespace suppression. (#217)
N216: Improve C template by using jinja2 macros and whitespace suppression. (#217)

- Replace for loops over argument lists with macros
- Use whitespace suppression `{%-` and `-%}` to allow better formatting
  of the template file without adding excessive whitespace to the
  generated code.

Closes #216.
jbcoe/C_API_generation,FFIG/ffig,FFIG/ffig,jbcoe/C_API_generation,jbcoe/C_API_generation,FFIG/ffig,FFIG/ffig,FFIG/ffig,jbcoe/C_API_generation,FFIG/ffig,FFIG/ffig,FFIG/ffig