add a clangd and qtcreator make targets

Add a clangd make target:
$ make clangd
This installs a .clangd file with configuration (includes/macros/compiler flags)
for the clandg language server.

Add a qtcreator make target:
$ make qtcreator
This installs a .qtcreator directory with QTCreator IDE project files.
In the QTCreator you can open a project by selecting the .qtcreator/tito.creator
file.

You can use 'make qtcreator' again to refresh .qtcreator/tito.files,
the rest of the project files will not be modified.

.templates/.clangd

@@ -0,0 +1,2 @@
+CompileFlags:
+  Add: [-pthread, -std=c++20, -I%%%CURRENT_DIR%%%/src, -I%%%GLOBAL_WORKING_DIR%%%/pikotools/src, -I/usr/include, -I/usr/local/include]