Should support relative link targets

[clue]

Centipede works fine while running on the root path like http://example.com/, however it does not correctly resolve relative href targets when running on a sub-path like http://example.com/demo.

Some test cases (incomplete):

/demo/ + a => /demo/a
/demo/ + /a => /a
/demo/ + ../a => /a
/demo + a => /a
/demo + /a => /a
/demo + ../a => /a

[umpirsky]

It's in another repository https://github.com/umpirsky/centipede-crawler. More precisely in https://github.com/umpirsky/centipede-crawler/blob/master/src/Centipede/Extractor/UrlExtractor.php. Thanks.