NULL instead of the passed-in setting if the specified path was not
found

cmake: use target properties to define shared/static defines

By applying them on the target, these are also available in the
installed libconfigConfig.cmake scripts

cmake: set VERSION + SOVERSION property on libraries

docs: fix simple typo, configuation -> configuration

add --disable-tests configure option

These properties are only active when the libraries are built as a shared library.

There is a small typo in contrib/ls-config/src/ls-config.c.

Should read `configuration` rather than `configuation`.

Addressing the issue #150

Fix typos in ls-config README.md

Detailed changelog (for all projects):
Fixed (disabled) "enable full optimization (/O2)" parameter in debug mode.
Added x64 platform and configured.
Added and configured two new build configurations: Debug_Static and Release_Static. These configurations provide static libraries with statically linked MSVC runtime (/MT and /MTd switches).
Depending on configuration, output files now have suffixes: Release - no (i.e. libconfig.lib), Debug - d (i.e. libconfigd.lib), Release_Static - s (i.e. libconfigs.lib), Debug_Static - ds (i.e. libconfigds.lib).
Redirected the output of intermediate build files to \temp\(Platform)\(Project)\(Configuration) to enable the possibility of error-free batch build.
Redirected the output of final build files to \build\(Platform).
Added postbuild event for all applicable examples to copy appropriate *.cfg files also into \build\(Platform).
Added few VS-related lines to .gitignore for convenience.

Add isString () convenience method

Pi value

Update the project, if you like my changes

Add option to override duplicate settings

Fix compilation of tests for out-of-tree-build

Fixed project version escape character

Fix memory leak when parsing invalid syntax

Add a destructor for TOK_STRING that is called when a TOK_STRING is
discarded during error recovery.
Closes #142.

`lib/grammar.c` was regenerated using "bison (GNU Bison) 3.0.4".

libconfig rejects settings with duplicate names by default.
With this option enabled, libconfig will instead remove the old
setting and add the new one.

We have to modify the include path, otherwise I get

| libconfig/tests/tests.c:31:10: fatal error: libconfig.h: No such file or directory
|    31 | #include <libconfig.h>
|       |          ^~~~~~~~~~~~~
| compilation terminated.
Signed-off-by: Bernhard Walle <bernhard.walle@ncp-e.com>

Fix to undo #120 and make Docker compatible

Add missing include in CMakeLists