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/meson.build

@@ -0,0 +1,24 @@
+ptprnt_hpps = files (
+    'libusbwrap/interface/IUsbDeviceFactory.hpp',
+    'libusbwrap/interface/IUsbDevice.hpp',
+    'libusbwrap/UsbDeviceFactory.hpp',
+    'libusbwrap/LibUsbTypes.hpp',
+    'libusbwrap/UsbDevice.hpp',
+    'interface/IPrinterDriver.hpp',
+    'interface/IPrinterTypes.hpp',
+    'P700Printer.hpp',
+    'PtouchPrint.hpp',
+    'graphics/Bitmap.hpp',
+    'graphics/Image.hpp',
+    'graphics/Monochrome.hpp'
+)
+
+ptprnt_srcs = files (
+    'PtouchPrint.cpp',
+    'P700Printer.cpp',
+    'graphics/Image.cpp',
+    'graphics/Bitmap.cpp',
+    'graphics/Monochrome.cpp',
+    'libusbwrap/UsbDeviceFactory.cpp',
+    'libusbwrap/UsbDevice.cpp',
+)