Invite page updated so you can have multiple active invite codes

Previously, the invite process was pretty annoying if you were planning to invite multiple people - you could only have one "active" invite code at a time, so you'd have to send someone a code and then wait until they registered before you could generate another code for the next person.

I've fixed this now and it's possible to have multiple active codes, so you can generate as many as you need (up to the limit of how many codes you've been granted). You can do this on the invite page: https://tildes.net/invite

Hopefully this makes it easier to invite people, and as always if you want more codes for a particular purpose just send me a message and let me know.