Set content-type and charset

[biryukovmaxim]

set content type header.
it's better for client to decode response, it's good also for debugging using sniffers

[Totodore]

Did you consider adding content types on other responses (for instance in error responses) ?

[biryukovmaxim]

Did you consider adding content types on other responses (for instance in error responses) ?

I thought I did it in the error handling pr. I checked and realized that I didn't.