Make botometer.Botometer.check_account() a function of our package

[ryantmoore]

As of commit 9f809e7, the user calls

x <- setup_botscan("a", ..., "e")
x$check_account("@...")

to use botometer. It would be better if we can make our own check_account() that could either

1. be exported from our own NAMESPACE and available when users library(botscan), or
2. be an internal function wrapped by our botscan()