feat(friends): adding getFriendsFromSource & avatar wrappers

[dan-myles]

Added a new function wrapper get_friends_from_source... Unfortunately the name is very misleading. This will not only get "friends" from the source (gameserver, lobby, chat room), but it will return all users. However the steamworks api has it named the same way so I thought I would keep it.

Also it requires a client to be connected to the source in order to work. Once connected you will be able to get all users on that particular gameserver etc.

[dan-myles]

i've gone ahead an added some more wrappers here for avatar. the steam api mentions the ability to pass in the steamid of the local users to get the current users avatar.

saw that this hadn't been implemented... as of right now we can only get avatars of "friends"

let me know what you think!