When scanning CMake module files for .rst comments, recognize
bracket comments starting in ".rst:" too. For example:
#[[.rst:
Include the bracket comment content terminated by the closing bracket.
Exclude the line containing the bracket if it starts in "#".
Teach the CMakeLib.testRST test to cover multiple bracket lengths
and ending brackets on lines with and without "#".
Update the cmake-developer.7 manual to document the bracket-comment
syntax for .rst documentation.