Use go.mod replace in sub modules to point to same version

Fix example go.sum

public method to check cors domain (rs#115)

Add CORS headers to non-preflight OPTIONS too (rs#85)

Non preflight OPTIONS requests should work with CORS too.
This change is removing abort in actual request CORS handler for
OPTIONS request, so the client can receive the necessary headers
on such request.

Use switch instead of if-else chain (rs#66)

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