add tab stops to snippets, plus a few bug fixes

snippets/pn2drum

@@ -6,8 +6,8 @@
 # --
 -- @pn2drum
 d'drum $ cf $ stack [
-  s "[hh*8 [hh*4 ho]]/2",
-  s "[~ [~ sn:1] ~ sn:1 ~ ~ sn:1 ~]/2",
+  s "[${3:hh}*8 [$3*4 ${4:ho}]]/2",
+  s "[~ [~ ${2:sn:1}] ~ $2 ~ ~ $2 ~]/2",
   -- every 4 (brak . density 2) $ -- (3)
-  s "bd*2" -- (1) "house*2" -- (2) "house(3,8)"
+  s "${1:bd}*2" -- (1) "${5:house}*2" -- (2) "$5(3,8)"
   ]