Previous glyph (Five Spoked Asterisk) looks great on Linux, but as it
turns out seems to be broken everywhere else. Use this opportunity to
point out, that SDL 1.2 in general is not being developed any more.
Also, make a correction:
"DOSBox does indicate support" -> "does not"
Information in comparison table is based on developer testing on Linux
and user reports on Windows.
Remove VS-related info from INSTALL file instead of duplicating it in
README.md.