Persist state

[juniorz]

This is what tor currently stores in the state file:

EntryGuard basilisk 62831916C678852C76D006482B04A17B0A9F8AF1 DirCache
EntryGuardAddedBy 62831916C678852C76D006482B04A17B0A9F8AF1 0.2.7.6 2016-01-09 22:15:42
EntryGuardPathBias 64.000000 62.000000 50.000000 9.000000 3.000000 6.000000
EntryGuardPathUseBias 31.000000 28.000000
...
EntryGuard 2c61bae6f99c715c 3B14BC970F0F27656A2418DD7BAF06B90A688885 NoDirCache
EntryGuardDownSince 2016-03-11 15:35:52 2016-03-29 23:56:49
EntryGuardAddedBy 3B14BC970F0F27656A2418DD7BAF06B90A688885 0.2.7.6 2016-01-29 20:28:45
EntryGuardPathBias 5.000000 5.000000 5.000000 0.000000 0.000000 0.000000
EntryGuardPathUseBias 2.000000 2.000000

We need to store USED_GUARDS, SAMPLED_UTOPIC and SAMPLED_DYSTOPIC.

For USED_GUARDS, we may need the same properties (addedBy, DownSince, pathBias, pathUseBias) in case we need to persist them (we know at least downSince is necessary).

But for the sampled sets I don't think it make sense to store anything but the node digests.

So the format would be:

UsedGuard  basilisk 62831916C678852C76D006482B04A17B0A9F8AF1 DirCache
UsedGuardDownSince 2016-03-11 15:35:52 2016-03-29 23:56:49
UsedGuard 2c61bae6f99c715c 3B14BC970F0F27656A2418DD7BAF06B90A688885 NoDirCache
UsedGuard philippe 12705256000C108C5327357798D9270B5AC8BF84 DirCache

and

SampledUtopicNode bastelfreak DF924196D69AAE3C00C115A9CCDF7BB62A175310
SampledUtopicNode aergia 342A1AC764D89248E66458C077CFF668D05FFF34
SampledDystopicNode fejk 2AFE920194ED5807377CB0BB696C5C870CED8BFD
SampledDystopicNode JojoTor1 47B596B81C9E6277B98623A84B7629798A16E8D5

[juniorz]

USED_GUARDS is persisted but it contains duplicate entries. I suspect when loading from state, we add things that are already in the list.