optimization: read stats once and remember it

optimization: read stats once and remember it

for an initial run and new commits this speeds stagit up a bit:
on an initial run of sbase goes from about 4 seconds to 2.8 on my machine.

now we can't use statsbuf, so create the stats string ourselves, while at it
color the + and - using a style (can be disabled for the color-haters out
there ;)).