Release v2.5.9

• Prefer parsing db from influxql instead of query parameter
• Fix prom_read uses a measurement name as a backend key as prom_write (#47) (Thanks @matianjun1)
• Optimize complex <db>.<rp>.<measurement> parsing
• Support pprof_enabled to determines whether the /debug/pprof HTTP endpoint is enabled
• Support to transfer data of all retention policies
• Optimize casting string in transfer (#27)
• Update github.com/golang/snappy from v0.0.3 to v0.0.4