Add stable release 0.F-3

[AllenJB]

stable_sha256 values taken from cataclysm-tiles.exe for 32-bit and 64-bit releases.

I noted recent 'number' values in the stable_assets list are using a dated tag, but couldn't see where this comes from / how it's worked out. I used the 'Build Number' from VERSION.txt as older releases appear to do.

An entry in the BUILDING or CONTIRBUTING docs on adding stable releases might be helpful.