Add setMany proc

[Nycto]

This function is a faster way to set many pixels in a bitmap, as compared to individually setting each pixel, while still being safe. The speed comes from a few mechanisms:

1. Centralized bounds checking
2. Single read from getData
3. Operating on reading and writing entire words instead of individual bits
4. Separating iteration over the primary bitmap and the mask to improve cache hits
5. ensuring that the input array is divisible by 8 to avoid any bounds checking within the loop

The big caveat is that I wrote this assuming the above mechanisms would be faster, but I didn't test each of those assertions separately. Nor have I examined the generated code. There is definitely still speed that can be wrought from this method if someone cares to tune it further. For example, there is definitely some unnecessary branching in the generated code that could probably be eliminated.

[ninovanhooff]

What's holding this one up? I'd say it would be quite nice to tackle the one one advantage Lua has over Nim

[Nycto]

There has probably been some bit rot with this PR, and there may be some ideas about a better possible function signature.