Add a note in the README on the breaking change introduced by rs#57

Add go.mod file

Make aligncheck and megacheck happy

Update travis configuration

Implement Access-Control-Allow-Origin *

Use Access-Control-Allow-Origin: * when all origins are allowed and
AllowCredentials is false.

Fix rs#30

Return 200 if Passthrough is disabled (rs#26)

Return OK if passthrough is false