Prepare for release 0.6.0.
Prepare for release 0.6.0.

btcsuite/btcwallet,decred/dcrwallet,jrick/btcwallet,Roasbeef/btcwallet,jrick/dcrwallet,decred/dcrwallet,Roasbeef/btcwallet,Stash-Crypto/btcwallet,synrg-labs/btcwallet,btcsuite/btcwallet,synrg-labs/btcwallet,Stash-Crypto/btcwallet,jrick/dcrwallet,jrick/btcwallet