Allow optional = character in domain syntax

[meyagen]

(Sorry, accidentally deleted the branch for the previous PR again.)

WHOIS allows lookups in the form of =domain to single out domains registered with different registrars (e.g. gmail.com) and return its full lookup info.

Otherwise, simply looking up with domain (without the =) for certain domains will yield a notice from WHOIS to specify the search. For example, in looking up gmail.com, we get the following response:

Whois Server Version 2.0

Domain names in the .com and .net domains can now be registered
with many different competing registrars. Go to http:https://www.internic.net
for detailed information.

GMAIL.COM.BR
GMAIL.COM.DEADKNIFERECORDS.COM
GMAIL.COM.MY
GMAIL.COM.TEJAARH.COM
GMAIL.COM

To single out one record, look it up with "xxx", where xxx is one of the
records displayed above. If the records are the same, look them up
with "=xxx" to receive a full display for each record.

...

Specifying with = yields the info we need:

string(3620) "Domain Name: gmail.com
Registry Domain ID: 4667231_DOMAIN_COM-VRSN
Registrar WHOIS Server: whois.markmonitor.com
...