Improvement: --glx-swap-method & --fade-exclude

- GLX backend: Add --glx-swap-method, to reduce painting region if the
  driver uses exchange or copy buffer swaps. Untested.

- Add --fade-exclude, to disable fading on specific windows based on
  some conditions. Untested.

- Expose GLX backend options through configuration file. Add fetching of
  GLX backend options through D-Bus.

- Use NULL pointer instead of element count to delimit string arrays in
  parse_vsync()/parse_backend()/parse_glx_swap_method().

- Add documentation about "wintypes" section in configuration file.

compton.sample.conf

@@ -34,6 +34,7 @@ fading = true;
 fade-in-step = 0.03;
 fade-out-step = 0.03;
 # no-fading-openclose = true;
+fade-exclude = [ ];
 
 # Other
 backend = "xrender"
@@ -53,6 +54,13 @@ detect-transient = true;
 detect-client-leader = true;
 invert-color-include = [ ];
 
+# GLX backend
+# glx-no-stencil = true;
+glx-copy-from-front = false;
+# glx-use-copysubbuffermesa = true;
+# glx-no-rebind-pixmap = true;
+glx-swap-method = "undefined";
+
 # Window type settings
 wintypes:
 {