08_momentum.pl todo comment fixups
symbols.pm:  some symbols in the listing look like the following, where the thing on the far right is an expression, not a simple identifier; it doesn't matter, we don't care what the expression is.  that's just source code.  the byte that it resolved to is still there and that's what we want.  so make symbols.pm parse things like the following:
     62 U00ff             00 e0       terminal_velocity =  $ff - $1f   ; ie -$1f
... which sets terminal_velocity = 0xe0.
rework and write tests for the terminal velocity logic.  signed comparison logic makes sense but is a bit non-obvious.
also:  ooops, constants still need a # in front of them when using them as a literal/immediate.
turn terminal velocity way up in newbies.asm in response to testing.  waaay up.  dicked with gravity a bit but decided that a gravity of 1 looks best.
if you go in to the debugging and put your playery at 70, you now nicely float (plummet?  drop?) down and land on a platform.  woot!