Improvement #74: Use libevent for main loop

- Use libevent for main loop. I will explain the reasons in #56 later.
  The preferred libevent version is 2.x, yet 1.4.x should work as well.

- As a result, compton now should build fine on *BSD. Thanks to
  DachiChang for the FreeBSD build issue report.

- Another consequence is we now use microsecond-level timing all the
  way. Nanosecond-level code will be dropped soon. Start using long
  instead of unsigned long to represent time in milliseconds, as both
  can't hold the full epoch time in ms, anyway, and a signed type
  requires less care in subtraction. Wrap the epoch time in ms to 15
  days.

- Fix broken NO_VSYNC_DRM and NO_VSYNC_OPENGL compile-time options.

- Use git revision number for versioning in Makefile, and other small
  improvements.

- Reorganize struct _win. Drop unused w->damaged_sequence. w->damaged is
  turned to bool.

- Add type and format to winprop_t, as preparation for the new condition
  format.

- Add w->shadow_force and w->focus_force, to prepare for D-Bus support.

- Rename wid_get_prop() to wid_get_prop_adv() with more options. Add
  wrapper function wid_get_prop().

- Add some extra helper functions, for D-Bus support later.

- Make some functions return a bool value to indicate if it's
  successful.

- Modify add_win(), use a static const structure to initialize the new
  struct _win.

- Add some helper macros, like printf_err(f)(q). Make some errors fatal.

- Rename some types, constants, and functions. Code clean-up.

- Check for time disorder in paint_preprocess() when calculating fading
  steps.

- Rename evpoll() to swopti_handle_timeout(), and partially rewrite it.

- Make -h / --help legal.

- Known issue: compton segfaults on FreeBSD with nvidia-drivers, unless
  NO_VSYNC_OPENGL is used. Will look into it later. Thamls to DachiChang
  for reporting.
Bug fix #77 incorrect border_width handling & #73 window data issue

- (Hopefully) fix all incorrect handling of w->a.border_width in compton
  (#77). Thanks to baskerville for reporting.

- Attempt to fix #73 by correcting a mistake that window data is fetched
  from the wrong function. Thanks to zakkak.

- Add git commit/tag detection to Makefile for automatic versioning.

- Change -lGL linking order, to fix a segmentation fault caused by
  something in nvidia-drivers under FreeBSD, mentioned in #74. Thanks
  for the report from DachiChang.

- Link to -levent_core instead of -levent in Makefile. We might move to
  libev soon, though.

- Increase SWOPTI_TOLERANCE to handle the extraordinary delay of
  kqueue() under FreeBSD. Thanks for DachiChang's report.

- Add helper function dump_drawable() for debugging.

- Replace XInternAtom() calls with get_atom().

- Remove -lrt as it's unneeded.
Improvement: Use select() for main loop

- Back to using select() for main loop. Thus we are not longer relying
  on libevent.

- Add generic timeout system (untested) to prepare for D-Bus support.

- Drop troff man pages. Revise Makefile to improve documentation
  building, fix double LDFLAGS inclusion, and re-add -lrt. This turns
  asciidoc into a build time dependency.

- Change fading time calculation.

- Add --logpath and ostream_reopen() for debugging with -b.

- Drop unused lceil_ntimes() and other helper functions.

- Only very limited tests are done. Bugs to be expected.
Feature #75: Invert window color

- Add window color inversion (--invert-color-include). It means 2-3
  times extra painting, so performance issues are likely to appear.  I
  hope I could find a faster way to invert colors.

- Rename some functions.

- Fix update of some window properties after window type/data change.
  Hopefully this will be helpful for #73.

- Split win_build_picture() from win_blur_background().

- Correct memory leak of ps->focus_blacklist during reinitialization.

- Add win_upd_t and win_upd_run(), to reduce duplicate window property
  updates. But is unused right now.

- Limited tests are done overall. Bugs to be expected.
Bug fix #75: --invert-color-include not working & others

- Fix a small bug that breaks --invert-color-include if no other
  blacklists are present. Thanks to MaskRay and xiaq for reporting.

- Disable --unredir-if-possible for multi-screen setups.

- Fix a bug that causes --no-fading-openclose to have no effect in some
  cases. Add w->in_openclose to keep track of window open/close state.
Feature #80: D-Bus support

- Add D-Bus support. Currently 7 methods are available: "reset" (same as
  SIGUSR1), "list_win" (list the windows compton manages), "win_get"
  (get a property of the window), "win_set" (set a property of the
  window), "find_win" (find window based on client window / focus),
  "opts_get" (get the value of a compton option), and "opts_set" (set
  the value of a compton option), together with 4 signals: "win_added",
  "win_destroyed", "win_mapped", "win_unmapped".

- D-Bus support depends on libdbus.

- As there are many items and my time is tight, no much tests are done.
  Bugs to be expected.

- Create a new header file `common.h` that contains shared content.

- Fix some bugs in timeout handling.

- Update file headers in all source files.

- Re-enable --unredir-if-possible on multi-screen set-ups, as the user
  could turn if off manually anyway.

- Check if the window is mapped in `repair_win()`.

- Add ps->track_atom_lst and its handlers, to prepare for the new
  condition format.

- Known issue 1: "win_get", "win_set", "opts_get", "opts_set" support a
  very limited number of targets only. New ones will be added gradually.

- Known issue 2: Accidental drop of D-Bus connection is not handled.

- Known issue 3: Introspection does not reveal all available methods,
  because some methods have unpredictable prototypes. Still hesitating
  about what to do...

- Known issue 4: Error handling is not finished yet. Compton does not
  always reply with the correct error message (but it does print out the
  correct error message, usually).
Bug fix #84: Root window not repainted sometimes on wallpaper change

- Fix a bug that root window is not repainted on wallpaper change unless
  an Expose X event is received. Seemingly, if there's no mapped window
  on a screen, X will not send an Expose event when the wallpaper
  changes. Thanks to baskerville for reporting.

- Fix a X Pixmap leak when there's no existing wallpaper pixmap found.

- Fix a bug in mstrncpy() that null character is not added to the end of
  the copied string.

- Make VSYNC_STRS public, for use in src/dbus.c. Adjust the type of
  WINTYPES array. Add NUM_VSYNC.

- Add more targets for various D-Bus methods. Add "bad_target" D-Bus
  error. Improve error handling. Add more helper functions to append
  arguments to a D-Bus message. Add Introspect method to D-Bus
  introspection reply.

- Add public declarations of things in the new condition format code to
  common.h. Move definitions of some inline functions from compton.h to
  common.h. Make some functions public. Move wid_get_prop_adv() to
  compton.c. The primary code files of the new format src/c2.{c,h} will
  be published when ready.

- Add support for dumping version string in Makefile (make version), to
  make snapshot generation easier.

- Add repeated inclusion protection to common.h.

- Update documentation.

- Use gsed instead of sed in dbus-examples/cdbus-driver.sh if possible,
  as some BSD systems does not come with GNU sed by default. Thanks to
  DaChiChang for reporting.

- Code clean-up. Small type changes in register_cm() to silence
  warnings. Quit on failure in parse_vsync(). Apply stricter checks in
  force_repaint().