Bug #14: Completed quoting for parameters of some CMake commands

A wiki article pointed out that whitespace will only be preserved for parameters
in CMake commands if passed strings will be appropriately quoted or escaped.
http://cmake.org/Wiki/CMake/Language_Syntax#CMake_splits_arguments_unless_you_use_quotation_marks_or_escapes.

Quoting was added so that more places should also handle file names correctly
which contain space characters or semicolons eventually.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #15 from elfring/Complete_quoting_for_parameters_of_some_CMake_commands

Complete quoting for parameters of some CMake commands.
Added open content
Added test which selects count()
Renamed named_expression to selectable
Minor cleanup
Fixed serialization of multiple dynamic query elements.
Added static assert to give clearer error message for dynamic_xy
Merge branch 'release/0.28'
Merge tag '0.28' into develop

CppCon-Release:
- fixed bugs found during preparation for the talk
- added examples for the talk
- aggregator functions cannot be used in where() anymore (thanks to Arthur O'Dwyer for finding that in the open content session)
- fixed serialization of dynamic query elements (the separator was missing, thanks to Paul Körbitz for finding that)
- several minor cleanups