Add Configuration Option to Limit Redirects

[istr]

When testing for stale / outdated links it is very helpful to fail on redirects.

I propose to add a RedirectLimit option (as int value) with the following semantics

• unset or negative value: use the default limit built into net/http
• positive value: limit allowed number of redirects

Setting this to 0 would result in a failure for redirected links.

I will prepare a PR for this shortly.

[wjdp]

Implemented in #205