Add domain directory in bySiteStructure filenameGenerator

[s0ph1e]

Resources from different domain should not be mixed in one folder.

Actual behavior

• / => DIRECTORY/index.html
• /about => DIRECTORY/about/index.html
• https://another-site.com/about => DIRECTORY/about/index.html (same as prev!)

Should be changed to

Need to save files from different domains to different subdirectories (like wget do). Assuming we are downloading site http://example.com:

• / => DIRECTORY/example.com/index.html
• /about => DIRECTORY/example.com/about/index.html
• https://another-site.com/about => DIRECTORY/another-site.com/about/index.html

[s0ph1e]

done in #213, will be released in 3.0.0 soon