title: Pandas dataframe column value case insensitive replace where <condition>
body: <p>Is there a case insensitive version for pandas.DataFrame.replace? <a href="https://pandas.pydata.org/pandas-docs/version/0.21/generated/pandas.DataFrame.replace.html" rel="noreferrer">https://pandas.pydata.org/pandas-docs/version/0.21/generated/pandas.DataFrame.replace.html</a></p>
  
  <p>I need to replace string values in a column subject to a case-insensitive condition of the form "where label == a or label == b or label == c".</p>