Support custom global settings via env (kontena#46)

Respond to /.well-known/acme-challenge requests using ACME_CHALLENGE_…

…* envs (kontena#44)

update haproxy to 1.8.3 (kontena#43)

Add option to disable h2 (kontena#42)

configure http-in if health uri or certs (kontena#41)

allow to enable accept-proxy via env (kontena#38)