Improve the regex of getSiteNameFromLink function
Improve the regex of getSiteNameFromLink function

1. There's no Programmers Stack Exchange site anymore. It has been replaced to Software Engineering and its URL is 'softwareengineering.stackexchange.com' which is already caught by the regex.
2. The Bitcoin site's URL is 'bitcoin.stackexchange.com' and not 'bitcoin.com', therefore it is already caught by that regex.
3. Mathoverflow is a special site, but it doesn't end in '.com', but in '.net', therefore it is moved to the second alternative
4. Positive lookahead is added to '.com' because the function is called to get the site name to use it in the API and API doesn't require '.com' at the end of sitenames. However, API doesn't accept 'meta.mathoverflow', but only 'meta.mathoverflow.net', so '.net' in second alternative doesn't have (?=).
soscripted/sox,soscripted/sox