expose fewer internals in packages, for easier software reuse

- prometheus is now behind an interface, they aren't dependencies for the
  reusable components anymore.
- some dependencies have been inverted: instead of packages importing a main
  package to get configuration, the main package now sets configuration in
  these packages. that means fewer internals are pulled in.
- some functions now have new parameters for values that were retrieved from
  package "mox-".

dns/dns.go

@@ -10,10 +10,11 @@ import (
 	"golang.org/x/net/idna"
 
 	"github.com/mjl-/adns"
-
-	"github.com/mjl-/mox/moxvar"
 )
 
+// Pedantic enables stricter parsing.
+var Pedantic bool
+
 var (
 	errTrailingDot = errors.New("dns name has trailing dot")
 	errUnderscore  = errors.New("domain name with underscore")
@@ -113,7 +114,7 @@ func ParseDomain(s string) (Domain, error) {
 // is not enabled. Used for interoperability, e.g. domains may specify MX
 // targets with underscores.
 func ParseDomainLax(s string) (Domain, error) {
-	if moxvar.Pedantic || !strings.Contains(s, "_") {
+	if Pedantic || !strings.Contains(s, "_") {
 		return ParseDomain(s)
 	}