Fix rust to netscape conversion

[mahlzahn]

See #41 for the equivalent in python.

• set https_only using the value of secure of the cookie
• set subdomain according to domain starting with .
• add prefix #HttpOnly_ to domain for http-only cookies

See, for instance, https://docs.cyotek.com/cyowcopy/current/netscapecookieformat.html for documentation of the netscape cookie format.