add dao which takes care about all CRUD operations on storage
remove blockchain state since everything is stored on change
remove storage operations from structs(entities)
move structs to entities package
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
* Fix#130: Wrong answer for RPC server method getaccountstate
- fixed RPC Server response
- fixed RPC Server tests
- remove unused package from go.mod
* add index and type checker
* fix review comments (thx @aprasolova)
* Implemented rcp method GetAccountState
* code clean up
* Removed empty line
* Used consistently github.com/pkg/errors package. Amended error message
* Get rid of fmt.Sprintf and use either errors.Errorf or errors.Wrapf
* cosmetic changes
