Do not use single quotes in the example config

This replaces single quotes for double quotes in the configuration
comments that refer to strings.
This was misleading since someone could took that comment as a valid
config entry, which is not.  One notable example was `backend = 'glx'`
which is not accepted by libconfig.

This also adds `;` for each default config values for consistency.

picom.sample.conf

@@ -70,7 +70,7 @@ shadow-exclude = [
 # Fade windows in/out when opening/closing and when opacity changes,
 #  unless no-fading-openclose is used.
 # fading = false
-fading = true
+fading = true;
 
 # Opacity change between steps while fading in. (0.01 - 1.0, defaults to 0.028)
 # fade-in-step = 0.028
@@ -168,7 +168,7 @@ focus-exclude = [ "class_g = 'Cairo-clock'" ];
 # example:
 #   blur-kern = "5,5,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1";
 #
-# blur-kern = ''
+# blur-kern = ""
 blur-kern = "3x3box";
 
 
@@ -190,12 +190,12 @@ blur-background-exclude = [
 # Specify the backend to use: `xrender`, `glx`, or `xr_glx_hybrid`.
 # `xrender` is the default one.
 #
-# backend = 'glx'
+# backend = "glx"
 backend = "xrender";
 
 # Enable/disable VSync.
 # vsync = false
-vsync = true
+vsync = true;
 
 # Enable remote control via D-Bus. See the *D-BUS API* section below for more details.
 # dbus = false
@@ -226,7 +226,7 @@ detect-client-opacity = true;
 # try detecting this with X RandR extension.
 #
 # refresh-rate = 60
-refresh-rate = 0
+refresh-rate = 0;
 
 # Use EWMH '_NET_ACTIVE_WINDOW' to determine currently focused window,
 # rather than listening to 'FocusIn'/'FocusOut' event. Might have more accuracy,
@@ -250,14 +250,14 @@ refresh-rate = 0
 # in the same group focused at the same time.
 #
 # detect-transient = false
-detect-transient = true
+detect-transient = true;
 
 # Use 'WM_CLIENT_LEADER' to group windows, and consider windows in the same
 # group focused at the same time. 'WM_TRANSIENT_FOR' has higher priority if
 # detect-transient is enabled, too.
 #
 # detect-client-leader = false
-detect-client-leader = true
+detect-client-leader = true;
 
 # Resize damaged region by a specific number of pixels.
 # A positive value enlarges it while a negative one shrinks it.
@@ -297,7 +297,7 @@ detect-client-leader = true
 # The opposing option is use-damage
 #
 # no-use-damage = false
-use-damage = true
+use-damage = true;
 
 # Use X Sync fence to sync clients' draw calls, to make sure all draw
 # calls are finished before picom starts drawing. Needed on nvidia-drivers
@@ -309,7 +309,7 @@ use-damage = true
 # See `compton-default-fshader-win.glsl` and `compton-fake-transparency-fshader-win.glsl`
 # in the source tree for examples.
 #
-# glx-fshader-win = ''
+# glx-fshader-win = ""
 
 # Force all windows to be painted with blending. Useful if you
 # have a glx-fshader-win that could turn opaque pixels transparent.