perf: utilize legacy url.parse() in url_for() & full_url_for()

[curbengh]

Continuation of #124

Ref: hexojs/hexo#3846

[coveralls]

Coverage decreased (-0.06%) to 95.395% when pulling bd99335 on curbengh:refactor-url-api into 71bbcc4 on hexojs:master.

[curbengh]

if (data.hostname && data.hostname !== sitehost) return path;

if (data.hostname) seems redundant, but it is necessary because new URL('path:withSemicolon', http://${siteHost}).hostname results in empty string ''. Adding that condition is avoid early exit and force it to process path with semicolon.

[SukkaW]

I notice config.url is added to the test case. So is it means after this PR we might not be able to handle undefined case? For isExternalLink(), it will return false when (!config.url) is true.

[curbengh]

Good point, now that I think about it, it's more accurate to throw an error if config.url is undefined/null, since full_url_for() and isExternal() wouldn't work.