And drop associated _pkg.dev remnants (refs. #307).
Original `dev` branch had two separate packages for public and private keys,
but those are so intertwined (`TestHelper` subpackage is a proof) that it's
better unite them and all associated code (like WIF and NEP-2) in one
package. This patch also:
* creates internal `keytestcases` package to share things with wallet (maybe
it'll be changed in some future)
* ports some tests from `dev`
* ports Verify() method for public key from `dev`
* expands TestPrivateKey() with public key check
- balancer / wif / http.Client could be with data race
- add getter / setter with sync.Mutex
- now http.Client is pointer
- now you can provide your http.Client to rpcClient
* func to get private key from raw bytes
* added function to create raw transfer tx
* fixes
* more fixes
* prettify code and comments; neoscan interaction put in dedicated files
* Started RPC package to allow querying balances and sending raw transactions for sc's
* integrate invoke cmd in cli
* bumped version
* added sendrawtransaction to the rpc client.
