You'd need to buildup your own database to store data over time since the backend mostly only stores the current state (except for trading history).
There are some libraries to talk to the backend node in JS, Ruby, Python and of course C++.
You can start here: http://docs.bitshares.eu/api

I think to be a legit and sexy crypto we need another block explorer. I know cryptofresh is cool but it's lacking some basic charts like "supply over time" also the volumes are not correct (at least for bitUSD:BTS).
Also, just a good idea to have a backup explorer.
I'd like to be involved in the creation of this blockchain explorer. Who wants to guide me?