Cleaned up build and header files

- Require libminios >= 0.5
- Remove old includes directory when installing
- Compile with -fno-builtin (avoids warnings about standard functions)
- Removed complex.h (now provided by Openlibm)
- Include cdefs.h from types.h (needed for __BEGIN_DECLS)
- Removed open from unistd.h (comes from fcntl.h)
- Removed assert.h and __assert_fail (provided by Mini-OS)
- Removed string.h (provided by Mini-OS)
- Removed cdefs.h (provided by Mini-OS)
- Added missing console.h includes (for printk)