Catch badmatch errors when using file:sendfile
Merge branch 'clean-set-max-conns-test' of git://github.com/fishcakez/ranch
Merge branch 'fix/sendfile-badmatch' of git://github.com/soundrop/ranch
Add Transport:sendfile/4,/5

Adds offset based sendfile to transports. Same behaviour as
file:sendfile/4,/5 except socket and file arguments are reversed and
either a raw file or a filename can be used.

sendfile/2,/4,/5 now compulsory callbacks in ranch_transport.