Release 0.7.0

What's new?

Features:

• Support windows users;
• Implement StringList;
• Implement methods such as __repr__, __str__, __len__, append, copy, counter, cycle, get, pop, repeat, set, size, to_list and union. By implementing List trait for StringList.
• Implement astype method for type conversion from or to a StringList;
• Implement apply, case, where and union_all methods;
• Implement counter method for NonFloatList.

Doc:

• Update the examples of Readme.md;
• Add ulist's introduction and features in Readme.md;

Misc:

• Rename the scala parameter num as elem because we have StringList now, and the name element makes more sense than a number;
• Rename union method as union_all;
• Implement NonFloatList trait for methods abstraction.