Use Crystal MIME registry

[Sija]

Thanks to crystal-lang/crystal#5765 we can use MIME registry freshly built-in into Crystal stdlib.

If the system the app is run on is lacking MIME database there's a need to manually register following types to keep BC with previous Kemal version (since they're missing from MIME::DEFAULT_TYPES):

MIME.register ".ico", "image/x-icon"
MIME.register ".otf", "application/font-sfnt"
MIME.register ".ttf", "application/font-sfnt"
MIME.register ".woff", "application/font-woff"
MIME.register ".woff2", "font/woff2"
MIME.register ".mp4", "video/mp4"
MIME.register ".webm", "video/webm"

[sdogruyol]

LGTM 👍 Could you please open a follow-up PR to https://github.com/kemalcr/kemalcr.com docs for adding custom Mime::Registry types. That'd be awesome 👍

[Sija]

@sdogruyol Sure! Could you point me please in the direction where exactly should I add it?

[sdogruyol]

@Sija adding it under Helpers in https://github.com/kemalcr/kemalcr.com/blob/master/guide.md would be 👌