Fix Logger and other build issues (#7)

This branch fixes a couple of issues with the build
- stop linking everything in a library which is then linked against a single main. It doesn't work the way I wanted. If functionality needs to be exposed by a library, it can be done later or with a separate target
- This should also fix spdlog
- Source files are now in a separate meson file using mesons files() feautre
- Improve coverage generation by adding a script generating html coverage reports. This will hopefully keep the motivation higher to create more unit tests
- Increase the code coverage a bit to demonstrate that statement above is not a fluke 😄

Reviewed-on: #7

src/main.cpp

@@ -16,10 +16,6 @@
     along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
  */
-
-#include <spdlog/common.h>
-#include <spdlog/spdlog.h>
-
 #include "PtouchPrint.hpp"
 
 int main(int argc, char** argv) {