Improve performance
Improve performance

- Prefer builtins where possible
  - Use builtin math for percent_of_total
  - Use parameter expansion instead of awk where possible
  - Query specific property that want for xprop instead of using awk
- Avoid extra call to get_window_manager
- Use xrandr's --current flag (doesn't poll for hardware changes; ~0.01 second vs. 0.075 seconds on my comupter)
- Get current monitor name from bspc directly without parsing

Addresses #36.

noctuid/tdrop,angelic-sedition/tdrop