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

Add modern *Config.cmake

These files will be generated and installed:

* libconfigConfig.cmake
* libconfigConfigVersion.cmake
* libconfig++Config.cmake
* libconfig++ConfigVersion.cmake

Add the `include(CheckSymbolExists)` to allow the usage of the `check_symbol_exists()` macro and fix #136

Add the `include(CheckSymbolExists)` to allow the usage of the `check_symbol_exists()` macro and fix #136

fix missing locales support macros in CMake

with autotools

cmake: remove lib prefix when building for non windows hosts

Add inline functions for readFile and writeFile for std::string

Fix portability problem due to == test

Add --disable-doc option

Improve the treatment of single line comment.

The "lib"-prefix is appended automatically for most non windows hosts.
Using the library name "libconfig" results in an .so file named
liblibconfig.so.

Instead, we use just "config" when the building for non windows hosts.

The "test" command, as well as the "[" command, are not required to know
the "==" operator. Only a few implementations like bash and some
versions of ksh support it.

When you run "test foo == foo" on a platform that does not support the
"==" operator, the result will be "false" instead of "true". This can
lead to unexpected behavior.

Make including library easier

libconfig can now be built by including with eg. add_subdirectory
directly, without changing compiler flags

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

Some changes for CMakeLists.txt - one bug-fix included