Version 0.4.0

We rapidly improved Koalas in documentation and added new functionalities in the past week. As of this release, all functions are documented. We also added the following features:

koalas:

• range (#254) - for generating a distributed sequence of data
• sql (#256) - for running SQL queries

koalas.DataFrame:

• merge (#264)
• to_json (#238)
• to_csv (#239)
• to_excel (#288)
• to_clipboard (#257)
• clip (#297)
• to_latex (#297)

koalas.Series:

• unique (#249)
• to_clipboard (#257)
• to_latex (#297)
• clip (#297)
• fillna (#317)
• is_unique (#325)
• sample (#327)

Along with the following improvements:

• Design Principles and Contribution Guide (#246, #255)
• DataFrame.drop now supports columns parameter (#253)
• repr and repr_html improvements (#258) - only shows top 1000 when the number of values/rows in DataFrame and Series exceed 1000.