refac: Iterator-based LongSpec

First and dirty implementation of LongSpec.Iterator.
Iteartors allow sequence coding, i.e. collapsing tokens that
go in incremental sequences: "!abc!abd!abe" -> "!abc!!"
Also added: chunked storage to use for really long LongSpecs.
Merge branch 'master' of github.com:gritzko/swarm
Naive Lamport clocks: seq+pid