Bug fix: Issue #43, better client window lookup

More details on the issue report.

- Look up the client window of a WM frame when it's mapped instead of when
  it's created, for better reliability.

- Fix a warning when building.
Misc: Clean up

- Add 4 helper free functions that free XserverRegion, Damage, Picture,
  and Pixmap.

- Rename w->shadow to w->shadow_pict. Add a bool member w->shadow to
  prepare for a future change.
Improvement: Change generating process of alpha_pict, etc.

- Change how w->alpha_pict is generated, in hope to boost performance,
  slightly, and as a step to eventually move handling code of most resources
  used when painting to paint_preprocess().

- Remove alpha_pict parameter of shadow_picture() as it's not
  necessary.

- Let window opacity affect frame opacity.

- Rename some members of struct _win.
Improvement: Change painting sequence

- Now compton paints windows from the lowest to the highest.  Warning:
  I'm not completely certain that the change won't introduce unexpected
  glitches. This commit may be revoked in the future.

- Remove w->border_clip since it's no longer needed.

- Correct a mistake in find_toplevel2(). (clang --analyze found it out.)

- Change "func_name()" prototypes to "func_name(void)". If I remember
  correctly, "func_name()" means you are remaining silent about this
  function's parameters instead of stating it has no parameter in ANSI
  C.

- Add timestamps to error messages.

- Suppress error messages caused by free_damage().
Improvement: Defer shadow picture generation

- Defer shadow picture generation to minimize interactions with X,
  hoping to boost performance.

- Fix a rendering issue caused by clip_changed in configure_win().
  Remove clip_changed altogether.

- Split generation of shadow picture from calculating its geometry.

- Cache width/height including borders in struct _win as it's frequently
  used.
Bug fix: Issue #23, notify-osd not rendered

More details in the issue report.

- Add ClientMessage detection to ev_name() and ev_window(), although we
  don't actually handle the event.
Improvement: Change fading mechanism

- Change fading mechanism for better modularity. Remove fade queue and
  use members in struct _win to record fading data. In contrast to
  previous commits, this one actually could make the program slower (but
  very slightly, hardly noticeable if your CPU is anywhere close to AMD
  K7). As this commit changes lots of things, bugs are to be expected.

- Currently -F does not do its job. -f actually equals -fF. (While in
  the past -F equals nothing and -f is just -f.) A fix will be made
  soon. I suppose it isn't hard.

- Add a preprocessor function paint_preprocess() and move all
  preprocessing code in paint_all() to it.

- Add window flag support but currently unused.

- Add DamageNotify handling to ev_window().

- I'm considering removing HAS_NAME_WINDOW_PIXMAP = 0 support as I
  couldn't see what it is good for. Nor do I know what CAN_DO_USABLE
  does. Basically all my changes ignore these cases.
Bug fix: Detect and mark WM windows as active

See chjj's comments on issue #39:
https://github.com/chjj/compton/issues/39#issuecomment-8533360

- Add a switch --mark-wmwin-focused that try to detect WM windows and
  mark them active.

- Fix a bug that causes BadDrawable, etc. if a window is mapped then
  immediately unmapped.

- Fix a bug in determine_evmask().

- Add a debug option DEBUG_CLIENTWIN.

- Force window repaint on window frame extent change.

- Code cleanup.
Feature: Issue #29: Alternative shadow blacklist implementation

- Add shadow blacklist feature, but a different implementation from
  nicklan's. 5 matching modes (exact, starts-with, contains, wildcard,
  PCRE) and 3 matching targets (window name, window class instance,
  window general class). Not extensively tested, bugs to be expected.
  It's slower for exact matching than nicklan's as it uses linear search
  instead of hash table. Also, PCRE's JIT optimization may cause issues
  on PaX kernels.

- Add dependency to libpcre. Could be made optional if we have a
  graceful way to handle that in Makefile.

- Some matching functions are GNU extensions of glibc. So this version
  may have troubles running on platforms not using glibc.

- Fix a bug that access freed memory blocks in set_fade_callcack() and
  check_fade_fin(). valgrind found it out.

- Use WM_CLASS to detect client windows instead of WM_STATE. Some client
  windows (like notification windows) have WM_CLASS but not WM_STATE.

- Mark the extents as damaged if shadow state changed in
  determine_shadow().

- Rewrite wid_get_name(). Code clean-up.

- Two debugging options: DEBUG_WINDATA and DEBUG_WINMATCH.

- As the matching system is ready, it should be rather easy to add other
  kinds of blacklists, like fading blacklist.
Improvement: Change window type detection

- Let window type detection start with the client window if there's one,
  in hope to enhance performance.

- Change get_wintype_prop() to fetch the property only once.

- Default to WINTYPE_UNKNOWN instead of WINTYPE_NORMAL if
  _NET_WM_WINDOW_TYPE is missing.

- Fix a mistake in calc_opacity().

- Add some items to .gitignore.

- Fix a typo in usage().
Misc: Fix two memory leaks

- Fix two small memory leaks. valgrind detects another memory leak
  possibly caused by XGetTextProperty(), probably a bug in libX11, I
  couldn't fix that one.

- Use predefined atoms in Xatom.h to replace a few XInternAtom() calls.
Feature: Configuration file parsing

- Add support for parsing configuration files using libconfig.
  (Dependency on libconfig could be made optional once we get some
  better building system.) Few tests has been done, bugs to be expected.
  compton searches for a configuration file mostly according to the XDG
  standard. Firstly the configuration file requested by --config, then
  $XDG_CONFIG_HOME/compton.conf (~/.config/compton.conf, usually), then
  ~/.compton.conf, then compton.conf under $XDG_DATA_DIRS (often
  /etc/xdg/compton.conf). A sample configuration file is supplied as
  compton.sample.conf. Configuration file syntax may change in the
  future.  Commandline switches has higher priority than configuration
  file, except for --shadow-exclude. Use --config /dev/null to
  temporarily disable configuration file.

- Fix a bug that causes windows to disappear or be partially rendered on
  opacity changes.

- Fix a bug that causes some windows to ignore -i (inactive_opacity) and
  --inactive-dim, caused by the default window type change in
  a5d9955ca4.
Feature: Wintype-specific options in configuration files

- Add support of window-type-specific options (fade, shadow, and
  opacity) in configuration file parsing. Syntax shown in
  compton.sample.conf.

- Replace wintype_name() with an array of window type names. Code
  clean-up.
add global options struct.
remove fade_time from options struct.