Implement missing bits for an external servertype

Make ServerListeners public and add two helper methods to get access
to the address they listen on. This is useful for tests (among other
things)

Also make DefaultConfigFile a var so it can be overridden by server
types.

Fix for invalid environment variable names used on windows that start…

Fix for invalid environment variable names used on windows that start with an equals symbol. Even though this contradicts the Microsoft docs.

Fixes https://forum.caddyserver.com/t/basic-caddy-installation-failing-on-automatic-https/472?u=matt

* * Added support for environment variables to 'templates' module.

* Fixed flaw in test caused by environment variable ordering during testing on CI.

* Updated some local variables to camel-case.

* Reverted changes to replacer as environment variables are processed elsewhere.

* Removed PrintEnv functionality in favour of documenting using template range.

Fix error which lead to skipping tests in 'errors.TestErrorsParse'

Check for duplicate status code entries in 'errors' directive

Add support for default (wildcard) error page

Now logging the request body

Also don't bother showing stdout output in same situation

Need to add the name to namesObtaining each time we use the ACME client.

If another ACME client is trying to solve a challenge for a name not
being served by Caddy on the same machine where Caddy is running, the
HTTP challenge will be consumed by Caddy rather than allowing the owner
to use the Caddyfile to proxy the challenge.

With this change, we only consume requests for HTTP challenges for
hostnames that we recognize. Before doing the challenge, we add the
name to a set, and when seeing if we should proxy the challenge, we
first check the path of course to see if it is an HTTP challenge;
if it is, we then check that set to see if the hostname is in the
set. Only if it is, do we consume it.

Otherwise, the request is treated like any other, allowing the owner
to configure a proxy for such requests to another ACME client.

Logging the request body if the Content-Type is application/json or
application/xml

* dist/init/linux-sysvinit: use kill -0 to test process status

* dist/init/linux-sysvinit: use service (as root) instead of /etc/init.d/

fix typo

* Rounding the latency in certain scenarios

* run gofmt