v1.3.4: Groupby Apply Enhancements

[jmcarpenter2]

• Enable indexing after a groupby, e.g. df.swifter.groupby(by)[key].apply(func)
• Improve groupby apply progress bar
  • Previously, the groupby apply progress bar only appeared after the data was distributed across the cores.
  • Now, the groupby apply progress bar appears before the data is distributed for a more realistic reflection of how long it took
• Additional groupby apply code refactoring and optimizations, including removing the mutability of the data within ray