Refactor: Moved README, ChangeLog, TODO files to docs/ folder + update Changelog. (#2036)

docs/CHANGELOG.txt

@@ -33,6 +33,21 @@ HOW TO UPDATE?
  VERSION 1.64 (in progress)
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+Changes:
+
+- Moved Readme, Changelog and Todo files to the docs/ folder.
+  If you are updating dear imgui by copying files, take the chance to delete the old files.
+- Added imgui_widgets.cpp file, extracted and moved widgets code out of imgui.cpp into imgui_widgets.cpp.
+  Re-ordered some of the code remaining in imgui.cpp in cleared chunks.
+  NONE OF THE FUNCTIONS HAVE CHANGED. THE CODE IS SEMANTICALLY 100% IDENTICAL, BUT ALL FUNCTIONS WERE MOVED.
+  Because of this, any local modifications to imgui.cpp will likely conflict when you update.
+  If you have any modifications to imgui.cpp, it is suggested that you first update to 1.63, then
+  isolate your patches. You can peak at imgui_widgets.cpp from 1.64 to get a sense of what is included in it,
+  then separate your changes into several patches that can more easily be applied to 1.64 on a per-file basis.
+- As a reminder, if you have any change to imgui.cpp it is a good habit to discuss them on the github
+  so a solution applicable on the Master branch can be found. If your company has changes that you cannot
+  disclose you may also contact me privately.
+
 
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  VERSION 1.63 (Released 2018-08-29)