colors

[sug0]

• Add im_initcolor_* methods for Color_t
• Add cap field to Color_t to prevent future wasteful memory allocations, namely in
  • if (unlikely(!dst->color || (dst->color && dst->size < sizeof(uint8_t)))) which should become...
  • if (unlikely(!dst->color || (dst->color && dst->cap < sizeof(uint8_t))))
  • New allocations should save the cap of the region
  • If Color_t is modified to contain a new type of color, then size should be updated in accordance with the storage used