Fix installation of headers

This is a first attempt at fixing issue #3.

What I've done is specifically

 * Move `create_types_arch_h` before `fill_makefile_wireframe` so that `types_arch.h` gets included in the `HEADERS` array.
 * Add a second `ARCHHEADERS` array for the headers in `arch/inline`.
 * Change the location where headers are installed to from `$(PREFIX)/include` to `$(PREFIX)/bsdnt/include`. This prevents naming collisions from generically-named headers like `config.h` and `sha1.h`.