Improved helper message for --lang option

The list of available (aka 'supported') languages is now printed in the
helper

mk_script.py

@@ -36,6 +36,13 @@ tmpl_ext = '.tmpl'
 config_header = '# Configure file for {}\n'.format(os.path.basename(sys.argv[0]))
 config_file = os.path.join(os.path.expanduser('~'),'.mk_script.cfg')
 
+# Supported languages helper
+for rootdir, dirs, files in os.walk(tmpl_dir):
+    supported_lang = ['.'.join(file.split('.')[:-1]) for file in files]
+supp_lang_str = '(avail: '
+supp_lang_str += ', '.join(supported_lang)
+supp_lang_str += ')'
+
 #------------------------------------------
 #-- Classes
 class Script:
@@ -97,7 +104,7 @@ class Script:
 def run(
         filename : 'file name of the script to create',
         author : 'author' = None,
-        lang : 'Script language to apply' = DEFT_lang,
+        lang : 'Script language to apply '+supp_lang_str = DEFT_lang,
         python_version : 'Python version (will be discarded in no-python context)' = DEFT_python_version,
         with_begin : 'include python "begins" lib (will be discarded in no-python context)' = DEFT_with_begin,
         with_license : 'Include license identifyer' = DEFT_with_license,