Convert builtin help to reStructuredText source files

Run the convert-help.bash script to convert documentation:

 ./convert-help.bash "/path/to/CMake-build/bin"

Then remove it.

Help/command/ctest_empty_binary_directory.rst

@@ -0,0 +1,12 @@
+ctest_empty_binary_directory
+----------------------------
+
+empties the binary directory
+
+::
+
+  ctest_empty_binary_directory( directory )
+
+Removes a binary directory.  This command will perform some checks
+prior to deleting the directory in an attempt to avoid malicious or
+accidental directory deletion.