doc: Trim .txt files trailing whitespace

via OSX: find . -name '*.txt' -exec sed -i '' -E 's/[[:space:]]+$//' {} +

doc/docs.txt

@@ -28,7 +28,7 @@ The documentation consists of several documents:
     builtin templating system.
 
 - | `Term rewriting macros <trmacros.html>`_
-  | Term rewriting macros enhance the compilation process with user defined 
+  | Term rewriting macros enhance the compilation process with user defined
     optimizations.
 
 - | `Internal documentation <intern.html>`_