Refactor automatic importing in snscrape.modules to something less hacky

Cf. #357

snscrape/modules/__init__.py

@@ -1,15 +1,17 @@
-import importlib
-import os
-import snscrape.base
+import pkgutil
+
+
+__all__ = []
 
 
 def _import_modules():
-	files = os.listdir(__path__[0])
-	for fn in files:
-		if fn.endswith('.py') and fn != '__init__.py':
-			# Import module if not already imported
-			moduleName = f'snscrape.modules.{fn[:-3]}'
-			module = importlib.import_module(moduleName)
+	prefixLen = len(__name__) + 1
+	for importer, moduleName, isPkg in pkgutil.iter_modules(__path__, prefix = f'{__name__}.'):
+		assert not isPkg
+		moduleNameWithoutPrefix = moduleName[prefixLen:]
+		__all__.append(moduleNameWithoutPrefix)
+		module = importer.find_module(moduleName).load_module(moduleName)
+		globals()[moduleNameWithoutPrefix] = module
 
 
 _import_modules()