Feat: support sort list-like attribute values by frequency

[SukkaW]

#86.

Support sort list-like attribute values by frequency.

Now sortAttributesWithLists configuration accept following values:

• alphabetical
• frequency

Old configuration true will be considered as alphabetical, thus no breaking changes being introduced.

[maltsev]

I think it'd be helpful to provide also some pros/cons of using alphabetical VS frequency.

[kidonng]

@maltsev AFAIK frequency based sorting (such as Huffman) is usually used in image compression. For text documents alphabetical based sorting is more common.