New listings and general market statistics

Since version 1.4.5 I have added a new function crypto_global_quotes() which retrieves global aggregate market statistics for CMC. There also were some bugs fixed.

Since version 1.4.4 a new function crypto_listings() was introduced that retrieves new/latest/historical listings and listing information at CMC. Additionally some aspects of the other functions have been reworked. We noticed that finalWait = TRUE does not seem to be necessary at the moment, as well as sleep can be set to '0' seconds. If you experience strange behavior this might be due to the the api sending back strange (old) results. In this case let sleep = 60 (the default) and finalWait = TRUE (the default).