Issue #14783: Improve int() docstring and also str(), range(), and slice().

This commit rewrites the docstring for int() to incorporate the documentation
changes made in issue #16036.  It also switches the docstrings for int(),
str(), range(), and slice() to use multi-line signatures.
diff --git a/Misc/NEWS b/Misc/NEWS
index bc5470a..5cd69b4 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #14783: Improve int() docstring and switch docstrings for str(),
+  range(), and slice() to use multi-line signatures.
+
 - Issue #15379: Fix passing of non-BMP characters as integers for the charmap
   decoder (already working as unicode strings).  Patch by Serhiy Storchaka.