Version 0.13.0

We rapidly improved and added new functionalities in the past week. We also added the following features:

koalas.DataFrame:

• diff (#562)
• shift (#562)
• round (#537)
• rank (#546)
• any (#568)
• all (#568)

koalas.Series:

• diff (#564)
• quantile (#566)
• shift (#563)
• is_monotonic (#560)
• is_monotonic_increasing (#560)
• is_monotonic_decreasing (#560)
• round (#537)
• rank (#546)