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/include_regular_expression.rst

@@ -0,0 +1,18 @@
+include_regular_expression
+--------------------------
+
+Set the regular expression used for dependency checking.
+
+::
+
+  include_regular_expression(regex_match [regex_complain])
+
+Set the regular expressions used in dependency checking.  Only files
+matching regex_match will be traced as dependencies.  Only files
+matching regex_complain will generate warnings if they cannot be found
+(standard header paths are not searched).  The defaults are:
+
+::
+
+  regex_match    = "^.*$" (match everything)
+  regex_complain = "^$" (match empty string only)