Improvement: Change in client window lookup & wintype detection

- Revert to WM_STATE for client window lookup, as WM_CLASS is
  unreliable, either, but set the client window of an override-redirect
  window to itself.

- Conform to EWMH to make assumptions about window types when
  _NET_WM_WINDOW_TYPE is not available.

- Remove determine_wintype() and completely rely on client window for
  window type detection.
Misc: #49: Add CPack configuration

Add CPackConfig.cmake for generating binary packages (.tar.bz2, .deb,
.rpm) automatically. Pretty ugly, but mostly working.
CPackSourceConfig.cmake isn't ready yet.
Misc: #49: Add CMake support

Add CMakeLists.txt to support building with CMake, as @pvanek requests.
The old Makefile system and CPackConfig.cmake are still usable. (Of
course, make sure you don't overwrite them by executing cmake.) There
must be a bunch of bugs in CMakeLists.txt. :-) Let chjj decide which one
he will choose, here I keep both.
Improvement: Support reading _NET_WM_OPACITY from client windows

- Some WMs don't respect Keith Packard's proposal of
  _NET_WM_WINDOW_OPACITY, and do not copy _NET_WM_OPACITY attribute of a
  client window to its frame windows, thus cause opacity set by
  non-override-redirect windows to have no effect. This commit adds
  support for reading _NET_WM_OPACITY from client windows if running
  with --detect-client-opacity. Thanks to pvanek for reporting.

- Change Makefile logic to determine options from 3 variables
  (NO_LIBCONFIG, NO_REGEX_PCRE, NO_REGEX_PCRE_JIT) instead of CFG to
  ensure compatibility when we add new options. CFG variable is no
  longer been respected.
Feature: #7: VSync

- Add VSync feature. 3 possible VSync methods available: "sw" (software,
  not too reliable, but at least you have something to fallback to),
  "drm" (using DRM_IOCTL_WAIT_VBLANK, should work only on DRI drivers),
  "opengl" (using SGI_swap_control extension OpenGL, might work on more
  drivers than the DRM method). "sw" and "opengl" are briefly tested,
  "drm" received utterly no test (because I use the nVidia binary blob).
  They are enabled with "--vsync sw" / "--vsync drm" / "--vsync opengl".

- Add --refresh-rate to let user specify a refresh rate for software
  VSync, in case the automatic refresh rate detection does not work
  well.

- Seemingly the automatic refresh rate detection using X RandR in
  software VSync detects refresh rate incorrectly. Need further investigation.

- Fix a few bugs in fading timing.

- Add a workaround for client window detection on Fluxbox, as Fluxbox
  (incorrectly?) sets the override-redirect flag upon all frame
  windows.

- Software VSync adds dependency on librt (a part of glibc) for
  nanosecond-level timing functions, and libXrandr for automatic refresh
  rate detection; DRM VSync adds dependency on libdrm to use its drm.h,
  but does not link to libdrm; OpenGL VSync adds dependency on libGL.

- Print timing information on DEBUG_REPAINT.
Misc: Code clean-up

- Fix a memory leak in register_cm().

- Print a warning message if argument of --vsync is invalid.

- Known bug: compton will probably freeze X if another compositing
  window manager is running and --vsync opengl is enabled, with
  nvidia-drivers-304.51. Probably an issue on the driver. I could see no
  workaround.
Improvement: Pregenerate alpha pictures

Pregenerate alpha pictures to save time when painting. Add --alpha-step
to control the step of alpha picture generation (the opacity difference
between two consecutively generated alpha pictures).
Improvement: Stop painting on regions of higher windows

Sort of reverts cdf7db750d, but implements in a different way. (Well,
maybe the pre-cdf7db750d way is actually better, if I'm willing to
sacrifice some precious code reusability.) Basically, trading CPU for
GPU, in an attempt to solve farseerfc and ichi-no-eda's problems. Highly
experimental, could be revoked at any moment.
Bug fix #55: Workaround for window type detection on Openbox menus

A small workaround for a small problem.
Misc: Drop support for old versions of libXcomposite

Basically dropping support for HAS_NAME_PIXMAP = 0 because I don't think
there are many people using it, and I cannot maintain it. CAN_DO_USABLE
support is under evaluation.
v0.0.1