Imports of package cache

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
errorsPackage errors implements functions to manipulate errors.
github.com/google/certificate-transparency-go/trillian/ctfe/cache/lruPackage lru defines the IssuanceChainCache type, which implements IssuanceChainCache interface with Get and Set operations.
github.com/google/certificate-transparency-go/trillian/ctfe/cache/noopPackage noop defines the IssuanceChainCache type, which implements IssuanceChainCache interface with Get and Set operations.
timePackage time provides functionality for measuring and displaying time.