usemodules.pl and usemodules.py should be merged into a single tool

[vmagnin]

For historical reasons, two usemodules.* scripts were written.
The Perl version is installed by CMake as a tool for users:
-- Installing: /usr/local/bin/gtk-3-fortran-modscan
The Python version is not installed by CMake and is simpler but has an interesting feature: detection of deprecated functions (based on information in the gtk-fortran-index.csv file). And it is used by sketcher/gtkf-sketcher.f90 (which should also be installed by CMake).

It would be better to merge the features of those two tools into a single one, either a Perl script or a Python one.

[vmagnin]

$ ./usemodules.pl --help

Scan Fortran source files for GTK and related library
functions and generate the required USE statements.
Note that only one set of USE statements is generated for each
source file, even if it contains several program units.
Enumerator constants are found if the list is present.

Usage:
 ./usemodules.pl [--csv=<file> --out=<file> --enum=<file> --help --[no]link] [files]

--csv      Specify the CSV file with the function list [gtk-fortran-index.csv]
--out      Specify the output file for the use statements [gtk-modules.txt]
--enum     Specify the file with the list of constants [gtk-enumerators.lis]
--help     Print this message
--[no]link Specify whether to scan symbolic links (only applicable when
           scanning a directory) [yes]
files      A list of files to scan. If empty then look at all Fortran
           sources in the current directory. If a single directory is
           given, then all Fortran files in that directory are checked.

[vmagnin]

$ ./usemodules.py --help
usage: usemodules.py [-h] dir_path

This program scan all the Fortran files in the given directory and subdirectories to generate a usemodules.txt file with
USE statements you can paste in your gtk-fortran programs. It also print warnings if you use deprecated GTK functions, and
finally displays all the GTK functions used in a directory.

positional arguments:
  dir_path    Path of the directory to scan

optional arguments:
  -h, --help  show this help message and exit

GPLv3 license, https://github.com/vmagnin/gtk-fortran