New source code extensions

This adds colors for the following extensions.

* C
  * .ii
* C++
  * .C, .cp, .cxx, .c++, .ii, .H, .hpp, .hxx, .h++, .tcc
* Fortran
  * .f, .for, .ftn
* Assembly
  * .s, .S, .sx
* Obj-C
  * .M