* Part of coniks-sys#151

* Add client-auditor messages

* Create audit log structure, query API finished

* Add/Update docs to include auditor, add ReqUnknownDirectory auditor error

* Use single generic verifySTRConsistency to be used by client and auditor

* Add tests for audit log, debug audit log

* Add assertions to validate auditor messages on client

* Add generic STR response handler

* # This is a combination of 2 commits.
# The first commit's message is:

Add TODO to move all generic STR auditing code to a separate module

# The 2nd commit message will be skipped:

#	Use single generic verifySTRConsistency to be used by client and auditor

* Fix documentation

* Use DirSTR instead of merkletree.SignedTreeRoot in auditlog

* Remove all references to auditor-directory communication, make auditor response message generic

* STRList -> STRHistoryRange

* Fail sooner in GetObservedSTRs

* Revert changes to protocol/str.go

* Always request epoch range in AuditingRequest, fix Insert() bug

* Index audit log by hash of directory's initial STR

* Insert latest STR into snapshot map right away

* Fix go vet error

* Change audit log index from byte array to string

* Add test case for getting an STR after an audit log update

* Refactor common functions

* Use slice for initial history inserted, remove IsKnownDirectory

* dirName --> addr, some documentation fixes

* Small fixes

* Revert "Change audit log index from byte array to string"

This reverts commit 7e54087.

Conflicts:
	protocol/auditlog.go

* More fixes for reverting