Release 4.0

- Significantly improved multi-screen experience:
    - Windows are now returning back to their preferred screen after connecting it back
    - Destination tag now corresponds to the original one during screen destroy phase
    - Fix issue with screen_select() after changing screen topology

- Improved Expose module a lot:
    - Use XComposite extension to properly make hidden windows screenshots
    - Use get_image_data_rgba() to properly handle BGRA colorspace
    - Expose module edge-cases optimization with zero and one visible windows
    - Other small cosmetic changes

- Made numerous improvements related to mouse pointer events and position:
    - Rework Window->focus() to show transients of maximized window
    - Prevent EnterNotify on focus_cycle() to visit every window
    - Prevent EnterNotify unmaximizing a window
    - Fix race condition with EnterNotify mapping floating windows
    - Fix race condition with focus during maximized windows startup
    - Improve focus logic for multiple screens (see comment in f364d604e)
    - Fix rapid EnterNotify preventor to avoid race condition on tag switching
    - Prevent rapid FocusIn events firing on EnterNotify and tag_select()
    - Avoid warp_pointer if the window already owns it
    - Implement tag->{focus} to select focus window on tag switching
    - Fix leaked reference of always_on window in Tag->focus

- Reworked focus_prev functionality keeping a list of previously focused windows:
    - Make focus_prev keep five instead of two last windows
    - Fix issue calling focus_prev() to some window below maximized one
    - Fix focus_prev behaviour inside FocusIn handler
    - Fix focus_prev focus stealing and tag switching

- Made mouse-based window movement and resize smoothier giving those actions more CPU time.

- Implemented feature to respect WM_SIZE_HINTS for newly created windows making dialogs look prettier.

- Updated X11::XCB to 0.23 to use brand new shiny features.

- Started several markdown documents, especially Development.md describing korgwm history.

- Slightly updated default config:
    - Rebind Fn keys to Mod+Alt because of a ThinkPad bug
    - Make pointer follow the window during win_move_tag()
    - Change Mattermost screen affinity
    - Support KORGWM_DEBUG_PORT environment variable to avoid EADDRINUSE starting second korgwm instance
    - Rename workspace names using only numbers

- Other minor improvements and fixes:
    - exec() now tries to open STDIN, STDOUT, STDERR to /dev/null after closing them
    - Add some fairness to X events poller
    - Add doc/release_checklist.md describing the release procedure
    - Implement KORGWM_DEBUG_API to enable debug API calls regardless debug config
    - Implement dump_screens() debug API call
    - Update .xinitrc to avoid several freezes and other issues
    - Ignore "Window errors" caught when closing multiple windows at a time
    - Replace redundant splice with grep
    - Fix issue with pointer not warped on a maximized window
    - Fix shameful memory leak inside Window DESTROY routine
    - Fix typo in focus->{window}
    - Add Gtk3::disable_setlocale() to avoid 0.5 value interpreted as 0