v0.20.0: Update versions (#258)

* Update version to v0.18.0

* Refactor module interface
Move `mnemonic` to public`

* Fix linter warnings
Add docs

* Fix source code formatting

* Remove 32bit builds for Appveyor

* Update rocksdb version

* FIx travis config for rustfmt

* Remove rust beta channel from travis CI

* Move to stable formatter

* TravisCI: allow failures on nightly

* Remove MacOS & update version for rocksdb

v0.19.0

• HD path parsing fixes
• Minor upgrades

v0.18.1

• Public mnemonic module
• Linter warning fixes
• Refactored module structure

v0.18.0

• Added support for BIP32 key derivation functionality,
  to provide private key generatiionnn from mnemonic passphrase
• Minor fixes and improvements

Added support for BIP39 mnemonics

Mnemonic generation based on BIP39

Add support for contract storage

• Add support for contract storage
• Minor bug fixes

Fixes for JSON RPC calls to support Ledger HD wallet

Fixed functionality for JSON-RPC to support Ledger HD wallet keyfile operations (import/export, list, shake, update)

Support for Ledger HD wallet

• Added signing of transaction with Ledger through JSON-RPC
• Import/export of keyfiles for HD wallet

Minor fixes for RPC mechanism

Merge pull request #178 from r8d8/issue/add_tests

"Morden" as chain name produces incorrect rlp of transaction

Emerald Vault 0.9 (Beta Release)

Switch back to offline cold storage mode, redesign from scratch JSON-RPC and CLI interfaces (more details).