Added HandleContext to re-enter soft-rewritten Requests.

[fbettag]

Dear gin committers, thanks for your great and awesome work. Unfortunately i've hit a corner case to which i didn't find a sufficient solution and would like to share my fix with the community.

We are rewriting a large pile of fu^Wold PHP Code from a project i just was put upon. The problem being that this is highly SEO-crap-stuff that the URLs that have been used in the past, need to work exactly like they are, because they have been pimped, yadda yadda blah.

Anyway, i could not convince them that using a better URL Scheme with 3xx would be probably better. So technically the problem is that they have URLs with multiple parameters within one /-segment. Imagine /:categoryName-at-:city . Now since i have all the categories and cities in the database, i tried adding them all, but that didnt work out to well as it took a few hours to load all categories for all the cities. Now i hot-fixed it to be /:category/at/:city and rewrite my Request in the NotFoundHandler and stick it back into gin with .HandleContext.

Hope this either gets merged or helps someone else.

[coveralls]

Coverage decreased (-0.3%) to 93.793% when pulling aeeb579 on fbettag:develop into f931d1e on gin-gonic:develop.

[fbettag]

i'll make a better one with tests and stuff. I also think there is still a bug in there which i can't quiet yet confirm. If someone could take a look at it. But this is deft. a feature missing.

[tboerger]

LGTM