Issue 300 oom

[sudachen]

I have implemented dump in two different ways: the first is the unsorted dump, in this way accounts are not sorted so is not required to load all of them to memory. This way consumes memory near to constant value with regarding to Go memory nature. The second way uses compact packing for storing accounts data to memory. It should dramatically reduce memory usage, however it will still take a lot space.

revised use: $ geth dump [unsorted] [hash|num],[hash|num],...,[hash|num] [address],[address],...,[address]

[splix]

It works! Took some time too, but exported a correct json

real	77m34.312s
user	25m12.260s
sys	12m46.284s

Sorted dump didn't finish in 2 hours, so I've cancelled it. And I think unsorted dump is enough, will cover most of the cases