Before this patch on block import we could easily be spending more than 6
seconds out of 30 in Uint256 encoding for UnspentBalance, now it's completely
off the radar.
commit methods duplicated putSmthIntoStore functions, but have MemCachedStore
now that can easily substitute for a Batch, especially given that interop
needs something like that for its storage purposes anyway.
The logic here is that we'll have all binary encoding/decoding done via our io
package, which simplifies error handling. This functionality doesn't belong to
util, so it's moved.
This also expands BufBinWriter with Reset() method to fit the needs of core
package.
