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/pikotools.creator
file.

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

.gitignore

@@ -4,13 +4,7 @@
 *.o
 src/pikotools.a
 tests/tests
-m
-.clangd
-.qtc_clangd/
-pikotools.cflags
-pikotools.config
-pikotools.creator
-pikotools.creator.user
-pikotools.cxxflags
-pikotools.files
-pikotools.includes
+/m
+/.clangd
+/.qtcreator/
+/.qtc_clangd/