Handle multiline options

Clean up options expecting lists before using them, as they may contain
newlines.

Examples:
* Enclosing command-line arguments in quotes may introduce newlines in
  option values:
  	$ codespell -S "A, B,
  	>               C, D, E"
* INI files may contain multiline values:
  	[codespell]
  	skip = A, B,
  	       C, D, E,

In all the above cases, the option parsing mechanism keeps the newlines
(and spaces). We need to clean up, by splitting on commas and stripping
each resulting item from newlines (and spaces).

Author: DimitriPapadopoulos

codespell_lib/_codespell.py

@@ -160,19 +160,15 @@ class QuietLevels:
 
 
 class GlobMatch:
-    def __init__(self, pattern: Optional[str]) -> None:
-        self.pattern_list: Optional[List[str]]
-        if pattern:
-            # Pattern might be a list of comma-delimited strings
-            self.pattern_list = ",".join(pattern).split(",")
-        else:
-            self.pattern_list = None
+    def __init__(self, pattern: Optional[List[str]]) -> None:
+        self.pattern_list: Optional[List[str]] = pattern
 
     def match(self, filename: str) -> bool:
-        if self.pattern_list is None:
-            return False
-
-        return any(fnmatch.fnmatch(filename, p) for p in self.pattern_list)
+        return (
+            any(fnmatch.fnmatch(filename, p) for p in self.pattern_list)
+            if self.pattern_list
+            else False
+        )
 
 
 class Misspelling:
@@ -1109,6 +1105,22 @@ def parse_file(
     return bad_count
 
 
+def flatten_clean_comma_separated_arguments(
+    arguments: Optional[List[str]],
+) -> Optional[List[str]]:
+    """
+    >>> flatten_clean_comma_separated_arguments(["a, b ,\n c, d,", "e"])
+    ['a', 'b', 'c', 'd', 'e']
+    >>> flatten_clean_comma_separated_arguments([])
+    >>> flatten_clean_comma_separated_arguments(None)
+    """
+    return (
+        [item.strip() for argument in arguments for item in argument.split(",") if item]
+        if arguments
+        else None
+    )
+
+
 def _script_main() -> int:
     """Wrap to main() for setuptools."""
     return main(*sys.argv[1:])
@@ -1256,7 +1268,7 @@ def main(*args: str) -> int:
 
     file_opener = FileOpener(options.hard_encoding_detection, options.quiet_level)
 
-    glob_match = GlobMatch(options.skip)
+    glob_match = GlobMatch(flatten_clean_comma_separated_arguments(options.skip))
     try:
         glob_match.match("/random/path")  # does not need a real path
     except re.error: