* minor changed to print
+ path.relative supports the array argument
* use the precodec.PATH_SEP now
* adjust code for the new path.relative supports
+ let the iterator remembers the last key
+ readStream, keyStream, valueStream interface
+ findStream/createFindStream(not ready)
* ensure iterator creation successful callback is always be called.
* minor changed to remove comments code
+ last event on readStream
+ [test] readStream last event
* adjust defalut SUBKEY_SEPS to optimize search
+ DontEscapeSep argument to encode function
* readStream
  + bounded(boolean, default is true) option to options: whether limit the boundary of the data.
  + separatorRaw(boolean, default: false): do not convert the separator, use this separator directly if true.
    in fact the pathStream is set the options to {separator:'/', separatorRaw: true, start:'0'} simply.
+ createPathStream/pathStream
* readStream/pathStream
  + the "last" event, this event will return the last raw key(hasnt be decoded).
    * the last return undefined if no more data.
  + the next option on options, this is a raw key ensure the readStream/pathStream return keys is greater than the key.
    * note: use this will replace the gt or lt(reverse) option.