Add \-continuation to CMake language quoted arguments

Teach the CMake language lexer to treat the \-LF pair terminating a
line ending in an odd number of backslashes inside a quoted argument
as a continuation.  Drop the pair from the returned quoted argument
token text.  This will allow long lines inside quoted argument
strings to be divided across multiple lines in the source file.
It will also allow quoted argument text to start on the line after
the opening quote.  For example, the code:

 set(x "\
 ...")

sets variable "x" to the value "..." with no opening newline.

Previously an odd number of backslashes at the end of a line inside
a quoted argument would put a \-LF pair (or a \-CR pair) literally
in the argument.  Then the command-argument evaluator would complain
that the \-escape sequence is invalid.  Therefore this syntax is
available to use without changing behavior of valid existing code.

Teach the RunCMake.Syntax test to cover cases of quoted arguments
with lines ending in \, \\, and \\\.  Odd counts are continuations.
cmake-developer.7: Improve flow of module documentation instructions

Use prose instead of enumerated steps and re-order the steps so that
the cmake-module directive is covered contiguously.
cmRST: Teach cmake-module directive to scan bracket comments

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.
Merge topic 'cmake-syntax-updates' into next

2945814 cmRST: Teach cmake-module directive to scan bracket comments
8bb2ee9 cmake-developer.7: Improve flow of module documentation instructions
efcf318 Add \-continuation to CMake language quoted arguments