Fix two bugs

[matheecs]

Fix to find correct misc directory and meshcat_example. Now, run the example by

git clone --recurse-submodules https://github.com/GiulioRomualdi/meshcat-cpp.git
cd meshcat-cpp
mkdir build && cd build
cmake ..
make -j
./example

[traversaro]

Hello @matheecs ! I think it is useful to separate the two fixes: the second one (add array include) is indeed a fix.

The first one is a bit tricky. Basically, at the moment meshcat-cpp is meant to be used when installed, and only linking the installed library. It is not meant to work by linking the library in the build directory. This is because some resources are found by looking at the appropriate relative location w.r.t. the location of the library, via reloc-cpp. Your change make the library work when it is used from the build directory, but it breaks the use of the library when installed, so it is not desirable. Two possible fixes are either:

• Option 1: Copy the files that are installed in <install_prefix>/share/meshcat-cpp/misc also in <build_directory>/share/meshcat-cpp/misc. In this way, also the build library will work fine, as it will look in ../share/meshcat-cpp/misc and find the required file. This is relativly simple, as it probably can be done by adding a few configure_file in the CMake script
• Option 2: Avoid to try to locate external files, and instead embed required files inside the library itself, using a resource manager such as cmrc. This option has the advantage that it would work fine also for static libraries.

fyi @GiulioRomualdi