Add support for removing newlines

This was tricky because of the nature of newlines. In actuality we
are removing Unix line feeds here (U+000A) because Windows carriage
returns are actually already removed by the string stripping in the
whitespace fix.

Creating the test case in Vim was difficult because I couldn't fig-
ure out how to manually enter a line feed character. In the end I
used a search and replace on a known pattern like "ALAN", replacing
it with \r. Neither entering the Unicode code point (U+000A) direc-
tly or typing an "Enter" character after ^V worked. Grrr.

csv_metadata_quality/app.py

@@ -25,6 +25,10 @@ def main(argv):
         # Fix: whitespace
         df[column] = df[column].apply(fix.whitespace)
 
+        # Fix: newlines
+        if args.unsafe_fixes:
+            df[column] = df[column].apply(fix.newlines)
+
         # Fix: unnecessary Unicode
         df[column] = df[column].apply(fix.unnecessary_unicode)