This should fix some crash bugs that could happen, I think as a result of pushing the camera out of bounds and then receiving mouse input before the camera gets fixed. The camera gets fixed immediately after it's changed, and there's some additional safety to prevent out of bounds access in the first place.
You can also toggle visibility of a later with the h key, and tileset definitions now support the w command, which defines a block to be a horizontal strip of four 8x8 tiles.