List the exchanges DataSinking covers. Returns exchange codes (bj / br / by / jpx / koe / ksc / lk / lse / nasdaq / np / nyse / otc / pk / rs / sse / szse / tpex / twse) with the number of reports available per exchange. Call this first to discover coverage. Sources: US = SEC EDGAR, A-shares = cninfo.com.cn, Japan = EDINET, Korea = DART, Taiwan = MOPS, UK = FCA NSM, Nepal = NEPSE, Brazil = CVM, Belarus = ЕПФР, Sri Lanka = CSE, Pakistan = PSX, Serbia = SEC register.