Add a streaming api to KeyRing and SessionKey (#131)

* barebone streaming functionality

* encryption needs to return a writecloser

* added eof check

* workaround for reader problem with copies

* separate mobile wrappers from main api

* add a clone in the read result to avoid memory corruption

* refactor to reuse code, and fix verification

* have to give the verify key at the start of the decryption

* enfore readAll before signature verification

* streaming api for SessionKey

* add split message stream apis

* name interface params

* fix streaming api so it's supported by go-mobile

* hide internal writeCloser

* fix nil access

* added detached sigs methods

* started unit testing

* unit testing and fixed a bug where key and data packets where inverted

* remove unecessary error wrapping

* figured out closing order and error handling

* add GC calls to mobile writer and reader

* remove debugging values and arrays

* writer with builtin sha256

* unit testing the mobile helpers

* comments and linting

* Typo in error

Co-authored-by: wussler <aron@wussler.it>

* Add GetKeyPacket doc

Co-authored-by: wussler <aron@wussler.it>

* Add rfc reference in comments

Co-authored-by: wussler <aron@wussler.it>

* small improvements

* add compatibility tests with normal methods

* remove unecessary copies in the tests

* update go-crypto to the merged changes commit

* update comments of core internal functions

* remove unused nolint comment

* group message metadata in a struct

* fix comments

* change default values for metadata

* change the mobile reader wrapper to fit the behavior of java

* remove gc calls in the wrappers to avoid performance penalties

* bring back the former Go2MobileReader to be used for ios

* Update crypto/keyring_streaming.go

Co-authored-by: wussler <aron@wussler.it>

* return an error when verifying an embedded sig with no keyring

* Update crypto/sessionkey_streaming.go

Co-authored-by: wussler <aron@wussler.it>

* linter error

* update changelog

* update changelog

Co-authored-by: wussler <aron@wussler.it>

go.mod

@@ -3,7 +3,7 @@ module github.com/ProtonMail/gopenpgp/v2
 go 1.15
 
 require (
-	github.com/ProtonMail/go-crypto v0.0.0-20210428141323-04723f9f07d7
+	github.com/ProtonMail/go-crypto v0.0.0-20210512092938-c05353c2d58c
 	github.com/ProtonMail/go-mime v0.0.0-20190923161245-9b5a4261663a
 	github.com/pkg/errors v0.9.1
 	github.com/stretchr/testify v1.4.0