Resolve "repo_name must not contain hyphens or other illegal characters and project_short_name is missleading"

Closes #3 (closed)

hooks/pre_gen_project.py

+import re
 import sys
 
-project_short_name = '{{cookiecutter.project_short_name}}'
+MODULE_REGEX = r'^[_a-zA-Z][_a-zA-Z0-9]+$'
+
+repo_name = '{{cookiecutter.repo_name}}'
+grammar_name = '{{cookiecutter.grammar_name}}'
 
 
 def main():
-    if not project_short_name.isalnum():
-        print('project_short_name "' + project_short_name + '" must be a single word. Exiting.')
+    if not re.match(MODULE_REGEX, repo_name):
+        print('Error: repo_name "%s" is not a valid URL and Java package name' % repo_name)
+        sys.exit(1)
+
+    if not grammar_name.isalnum():
+        print('Error: grammar_name "%s" must be a single word. Exiting.' % grammar_name)
         sys.exit(1)