Generate labels with pangocairo (#8)

Goal of this PR is to have some basic labels generated with pangocairo
- size of the canvas should be matching the input text and grow/shrink accordingly
- basic formatting options like fontsize and align should be working

Reviewed-on: moritz/ptouch-prnt#8

.vscode/c_cpp_properties.json

@@ -4,7 +4,7 @@
       "name": "Linux",
       "compilerPath": "/usr/bin/clang",
       "cStandard": "c11",
-      "cppStandard": "c++17",
+      "cppStandard": "c++20",
       "compileCommands": "${workspaceFolder}/builddir/compile_commands.json",
       "browse": {
         "path": ["${workspaceFolder}"]