Binary request support

[spikedboy]

Hi, good day.

I got mirage to crash with a binary request, of application/octet-stream content-type. I took a peak and it crashes when trying to read the body into a string. Would you be willing to support such requests in some way? To me it is good enough that it doesn't crash when handling them but I guess it would be nice if they would also be handled in some way, even though it wouldn't make much sense to match responses with requests of binary tipe perhaps? If not, would you be willing to accept a pull request for this issue somehow?

Cheers and thanks.