Fix back/forward slash in file path in mailabs formatter (#1938)

* mailabs formatter: back/forward slash in file path fix

* formatters.mailabs() path rework for Windows os

* new formatter added "mailabs_win"

* lint test fix commit

* mailabs_win: removed, mailabs: "/" replaced with os.sep for windows compatibility

* Black small style fix

TTS/tts/datasets/formatters.py

@@ -106,9 +106,9 @@ def mailabs(root_path, meta_files=None, ignored_speakers=None):
         meta_files (str):  list of meta files to be used in the training. If None, finds all the csv files
             recursively. Defaults to None
     """
-    speaker_regex = re.compile("by_book/(male|female)/(?P<speaker_name>[^/]+)/")
+    speaker_regex = re.compile(f"by_book{os.sep}(male|female){os.sep}(?P<speaker_name>[^{os.sep}]+){os.sep}")
     if not meta_files:
-        csv_files = glob(root_path + "/**/metadata.csv", recursive=True)
+        csv_files = glob(root_path + f"{os.sep}**{os.sep}metadata.csv", recursive=True)
     else:
         csv_files = meta_files