Fix tx decoding

v0.6.3

fix issue with tx decoding

v0.6.2

SQL driver update for crypto/Hash
Value can be nullable (Scan() accept null value)

Improve service tx, fix JSON.Marshal impl

v0.6.1

Improve service tx, fix JSON.Marshal impl

Update to exomum v0.12.1, internal improvements impl

v0.6.0

Update response structs, add new system api calls

v0.5.2

update interface