* sr25519

* added amino encoding

* fixed dependencies

* Apply suggestions from code review

Co-Authored-By: Tess Rinearson <tess.rinearson@gmail.com>
Co-Authored-By: Marko <marbar3778@yahoo.com>

* file structure

* Apply suggestions from code review

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

* address @melekes and @marbar3778 review

* removed nolint

* CHANGELOG and go-schnorrkel mod update

Refs #3262

## Issue:

Hey, not sure if this is disallowed for any reason specifically, but it would be very beneficial to define additional types to decode tendermint key implementations from bytes, since it uses a static codec. If this is okay, let me know and I will add documentation.

Context: For Ethermint to switch to using Cosmos' keybase, decoding the keys requires this codec to be updated

Just to document, I did experiment with creating a mapping from string to objects to be able to keep track of the key types added to be able to be used in the RegisterAmino(..) call, but because of how go is compiled, cosmos would just use the base types. This may be a useful feature for someone just building on top of Tendermint and not going through Cosmos, but to not add confusion or unnecessary complexity, I left it out.

## Commits:

* Exposes amino codec to be able to decode pk bytes in application

* Change how codec is modified

* Remove unneeded comment

* Fix comment

* Fix comment

* Add registered type to nametable

* Add pending changelog entry

* Reorder change

* Added check if type is registered and added test

* Make test type private

* Remove unnecessary duplicate exists check

* Don't use pointer receivers for PubKeyMultisigThreshold

* test that showcases panic when PubKeyMultisigThreshold are used in sdk:

 - deserialization will fail in `readInfo` which tries to read a
 `crypto.PubKey` into a `localInfo` (called by
  cosmos-sdk/client/keys.GetKeyInfo)

* Update changelog

* Rename routeTable to nameTable, multisig key is no longer a pointer

* sed -i 's/PubKeyAminoRoute/PubKeyAminoName/g' `grep -lrw PubKeyAminoRoute .`

upon Jae's request

* AminoRoutes -> AminoNames

* sed -e 's/PrivKeyAminoRoute/PrivKeyAminoName/g'

* Update crypto/encoding/amino/amino.go

Co-Authored-By: alessio <quadrispro@ubuntu.com>

This is intended for use in a future PR for #2414

* crypto/multisig: Pubkey -> PubKey

* crypto/encoding/amino: use pkg vars for routes

* crypto/multisig/bitarray

* crypto/multisig: ThresholdMultiSignaturePubKey -> PubKeyMultisigThreshold

* crypto/encoding/amino: add PubKeyMultisig to table

* remove bA import alias

https://github.com/tendermint/tendermint/pull/2255#discussion_r211900709

Signatures are now []byte, which saves on the number of bytes after
amino encoding

(squash this) address Ismail's comment

* crypto/secp256k1: Add godocs, remove indirection in privkeys

The following was previously done for creating secp256k1 private keys:

First obtain privkey bytes. Then create a private key in the
underlying library, with scalar exponent equal to privKeyBytes.
(The method called was secp256k1.PrivKeyFromBytes,
fb90c334df/btcec/privkey.go (L21))

Then the private key was serialized using the underlying library, which just
returns back the bytes that comprised the scalar exponent, but padded to be
exactly 32 bytes.
fb90c334df/btcec/privkey.go (L70)

Thus the entire indirection of calling the underlying library can be avoided
by just ensuring that we pass in a 32 byte value. A test case has even be written
to show this more clearly in review.

* crypto/secp256k1: Address PR comments

Squash this commit

* crypto: Remove note about re-registering amino paths when unnecessary.

This commit should be squashed.

Currently the top level directory contains basically all of the code
for the crypto package. This PR moves the crypto code into submodules
in a similar manner to what `golang/x/crypto` does. This improves code
organization.

Ref discussion: https://github.com/tendermint/tendermint/pull/1966

Closes #1956