Bump version to 2.1.5

Bump version to 2.1.4

Bump version to 2.1.1

bump version to 2.0.0

bump version to 1.9.0

modify changelog

bump version to 1.6.2

1. add one param(gasUniPrice) in utils.tx.generateRawUserTransaction …

…2.add encoding.stringToBytes && encoding.bytesToString

fix typo

bump version to 1.4.0