Add base currency option to BC,FX

[sgornick]

Currently !bc,fx defaults to using USD as the base currency (i.e., all the comparisons are in USD, e.g., 1 XAU = 1491.20 USD | 1 US dollar = 0.6976 euros)

I think it would be useful to specify a base currency and have the resulting exchange rates be calculated based on the base.

e.g. something like !bc,fx EUR would yield:
1 XAU = 1028.23 EUR | 1 euro = 1.45 US dollars, 1 euro = n.nn British pounds sterling, .... )

Additionally, I'ld like to see Bitcoin as one of the currencies returned.
1 eur = 1.10 bitcoins,

[nanotube]

btc already included.

also, dunno how much of a priority it is to output stuff in other currencies, since 90% of the BTC trade goes on in terms of USD...

[gary1961777]

Sounds good

[gary1961777]

Thats fine