Add core:image/bmp

[Kelimion]

Support for loading Windows + OS/2 BMP files.

• 1, 2, 4, 8, 16, 24 and 32 bpp
• Uncompressed, RLE4, RLE8 and Bit Field compression modes

Handles V3, V4, V5, OS/2 v1 + v2.x, and various truncated headers.

TODO(Jeroen):

• Right now all images are returned as 24-bit RGB. The core:image options to extend to RGBA (and use alpha where present) could be added, but RGBA bitmaps are very rare and not well supported (in other software).
• Add support to write 24-bit or 32-bit BMP with V4 header and default bit fields for 4-channel images, V3 header for 3-channel images.