Add `-i` flag (crawl inside path) and display an error on stderr if improper URLs are being given

[garlic0x1]

url.Parse does not return an error most of the time because it treats random strings as relative URLs.

[garlic0x1]

Just pushed another update that adds the -i flag for limiting the crawl to inside a path.
for example echo https://example.com/outer_path/path1 | hakrawler -i will not crawl https://example.com/outer_path/

[hakluke]

This is really great work, thanks garlic0x1 🙂