Imports of fetch_leaves command

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
encoding/hexPackage hex implements hexadecimal encoding and decoding.
flagPackage flag implements command-line flag parsing.
github.com/go-sql-driver/mysqlPackage mysql provides a MySQL driver for Go's database/sql package.
github.com/golang/glogPackage glog implements logging analogous to the Google-internal C++ INFO/ERROR/V setup.
github.com/google/trillian/storage/mysqlPackage mysql provides a MySQL-based storage layer implementation.