Refactor lookup functions names

[chimeno]

Currently there are at least three function for lookup bulk data: statuses, friendship and users.
Meanwhile two of them are called: lookup_friendshipand lookup_users the other one is called statuses_lookup. code.
I think is a good idea having all three in the same way, although we can fall in backward incompatibility, unless we proved a fallback.

Just saying.

[Aaron1011]

@chimeno: I agree. Which way do you think it should be? (changing statuses_lookup to lookup_statuses, or changing lookup_users and lookup_friendship? The lookup_friendship style looks better to me, but statuses_lookup is more consistent with the actual API structure.

[chimeno]

I'd go with the statuses_lookup approach due to it's more consistent with the actual API and with de twitter docs and urls, because the url is statuses/lookuplink.
Sorry for not coding a PR, right now I'm pretty busy but I'll try it.

@Aaron1011 Thanks for considering my opinion.

[ouattararomuald]

I agree with refactoring but just renaming functions will break compatibility between existing versions and upcoming. What i suggest is to mark existing functions with a decorator like Java's @deprecated which is used to explain why the method was deprecated and to suggest an alternative.