Improve variable declaration style

Separate declaration from initialization and add variable comments.

dotfiles/bash/post.bashrc

 ######################################################
 
 __bashum__lastrv() {
-    local rvfile="$RV_TMP/$$.lastrv"
-    local lastrv="$(cat "$rvfile")"
-    local do_rm=false
+    local rvfile        # path to return value cache file
+    local lastrv        # actual last return value
+    local do_rm         # true if we should remove the cache
+    rvfile="$RV_TMP/$$.lastrv"
+    lastrv="$(cat "$rvfile")"
+    do_rm=false
     test "$1" == "-r" && do_rm=true
     if [ "0$lastrv" -gt 0 ];
     then
 }
 
 __bashum__task_context() {
-    local ctx=$(task _get rc.context)
+    local ctx       # TaskWarrior context
+    ctx=$(task _get rc.context)
     test -n "$ctx" || return
     echo -n "|$ctx"
 }