volume: set volume in absolute value

Otherwise, it seems we can get a left/right imbalance when using
relative changes.

lib/volume.lua

@@ -13,13 +13,23 @@ local icons        = package.loaded["vbe/icons"]
 module("vbe/volume")
 
 local volid = nil
-local function change(what, how)
-   os.execute("amixer -q -D pulse sset " .. what .. " " .. how, false)
-   -- Read the current value
+local running = true
+local function current(what)
    local out = awful.util.pread("amixer -D pulse sget " .. what)
    local vol, mute = out:match("([%d]+)%%.*%[([%l]*)")
-   if not mute or not vol then return end
+   return vol, mute
+end
 
+local function change(what, how)
+   if how ~= 0 then
+      local vol, mute = current(what)
+      how = string.format("%d%%", vol+how)
+   else
+      how = "toggle"
+   end
+   os.execute("amixer -q -D pulse sset " .. what .. " " .. how, false)
+
+   local vol, mute = current(what)
    vol = tonumber(vol)
    local icon = "high"
    if mute ~= "on" or vol == 0 then
@@ -43,15 +53,15 @@ local function change(what, how)
 end
 
 function increase(what)
-   change(what, "2%+")
+   change(what, 2)
 end
 
 function decrease(what)
-   change(what, "2%-")
+   change(what, -2)
 end
 
 function toggle(what)
-   change(what, "toggle")
+   change(what, 0)
 end
 
 -- run pavucontrol