auto-sync: draw on idle to avoid flicker/tearing

st could easily tear/flicker with animation or other unattended
output. This commit eliminates most of the tear/flicker.

Before this commit, the display timing had two "modes":

- Interactively, st was waiting fixed `1000/xfps` ms after forwarding
  the kb/mouse event to the application and before drawing.

- Unattended, and specifically with animations, the draw frequency was
  throttled to `actionfps`. Animation at a higher rate would throttle
  and likely tear, and at lower rates it was tearing big frames
  (specifically, when one `read` didn't get a full "frame").

The interactive behavior was decent, but it was impossible to get good
unattended-draw behavior even with carefully chosen configuration.

This commit changes the behavior such that it draws on idle instead of
using fixed latency/frequency. This means that it tries to draw only
when it's very likely that the application has completed its output
(or after some duration without idle), so it mostly succeeds to avoid
tear, flicker, and partial drawing.

The config values minlatency/maxlatency replace xfps/actionfps and
define the range which the algorithm is allowed to wait from the
initial draw-trigger until the actual draw. The range enables the
flexibility to choose when to draw - when least likely to flicker.

It also unifies the interactive and unattended behavior and config
values, which makes the code simpler as well - without sacrificing
latency during interactive use, because typically interactively idle
arrives very quickly, so the wait is typically minlatency.

While it only slighly improves interactive behavior, for animations
and other unattended-drawing it improves greatly, as it effectively
adapts to any [animation] output rate without tearing, throttling,
redundant drawing, or unnecessary delays (sounds impossible, but it
works).

README.md

@@ -1,4 +1,4 @@
-Similar to [dwm-flexipatch](https://github.com/bakkeby/dwm-flexipatch) this st 0.8.3 (371878, 2020-04-30) project has a different take on st patching. It uses preprocessor directives to decide whether or not to include a patch during build time. Essentially this means that this build, for better or worse, contains both the patched _and_ the original code. The aim being that you can select which patches to include and the build will contain that code and nothing more.
+Similar to [dwm-flexipatch](https://github.com/bakkeby/dwm-flexipatch) this st 0.8.3 (4e90c0, 2020-05-09) project has a different take on st patching. It uses preprocessor directives to decide whether or not to include a patch during build time. Essentially this means that this build, for better or worse, contains both the patched _and_ the original code. The aim being that you can select which patches to include and the build will contain that code and nothing more.
 
 For example to include the `alpha` patch then you would only need to flip this setting from 0 to 1 in [patches.h](https://github.com/bakkeby/st-flexipatch/blob/master/patches.def.h):
 ```c
@@ -15,6 +15,8 @@ Refer to [https://st.suckless.org/](https://st.suckless.org/) for details on the
 
 ### Changelog:
 
+2020-05-20 - Upgrade to 4e90c0, 2020-05-09, removed visualbell 1, 2, 3 patches and force redraw after keypress due to incompatibility
+
 2020-04-20 - Upgrade to c279f5, 2020-04-19, and added the force redraw on pselect after key is pressed patch and the externalpipein patch
 
 2020-03-29 - Added invert and workingdir patches
@@ -75,8 +77,8 @@ Refer to [https://st.suckless.org/](https://st.suckless.org/) for details on the
    - [font2](https://st.suckless.org/patches/font2/)
       - allows you to add a spare font besides the default
 
-   - [force-redraw-after-keypress](https://lists.suckless.org/hackers/2004/17221.html)
-      - this patch forces the terminal to check for new data on the tty on keypress with the aim of reducing input latency
+   - [~force-redraw-after-keypress~](https://lists.suckless.org/hackers/2004/17221.html)
+      - ~this patch forces the terminal to check for new data on the tty on keypress with the aim of reducing input latency~
 
    - [hidecursor](https://st.suckless.org/patches/hidecursor/)
       - hides the X cursor whenever a key is pressed and show it back when the mouse is moved in the terminal window
@@ -120,8 +122,8 @@ Refer to [https://st.suckless.org/](https://st.suckless.org/) for details on the
    - [vertcenter](https://st.suckless.org/patches/vertcenter/)
       - vertically center lines in the space available if you have set a larger chscale in config.h
 
-   - [visualbell](https://st.suckless.org/patches/visualbell/)
-      - adds visual indicators for the terminal bell event
+   - [~visualbell~](https://st.suckless.org/patches/visualbell/)
+      - ~adds visual indicators for the terminal bell event~
 
    - [workingdir](https://st.suckless.org/patches/workingdir/)
       - allows user to specify the initial path st should use as the working directory