Added some missing #include's that may prevent compilation
BitSet class: Superficial changes
Image::BufferScratch: Dedicated bool template class

Prior version was relying on initialising a bool[], which is not terribly well-defined, may have been allocating more memory than necessary, and made me generally uncomfortable.
This version shares exactly the same functionality, and is still created using Image::BufferScratch<bool>, but explicitly forms a uint8_t[] for the raw data.