Minimal amount of changes needed to switch to GO 1.11
* crypto/internal/cipherhw was removed and internal/cpu was introduced
* wrong code formatting in handhsake_server_test.go was breaking
  the build

Implements two tests for SIDH/P503-X25519 interoperability. BoringSSL
initiates connection to TRIS and TRIS initiates connection to BoringSSL.
SIDH server always listens on port 7443

* SIDH/P503-X25519
* adds interop tests

serverHandshakeState::readClientHello was setting selected ALPN protocol
always on hs.hello.alpnProtocol, which is specific to TLS 1.2 and older.
Because of that server was marshalling ALPN to SH instead of EE.

see RFC7627

* includes AD in authentication check of TLS records

As per 5.2 of TLS 1.3 draft-28, the additional data is record header.

* tests: Update tests in order to support draft-28

* Interoperability: Updates NSS and BoringSSL versions to the
  one supporting draft-28
* Bogo: Updates revision number to use tests for draft-28
* FIX: makefile was using test-compat target instead of
  test-interop

* DC test: constify

* Use binary interface to encode in big-endian

* Changes tests so that they pass with draft-23
* BoringSSL interoperability: uses code at most recent commit. It uses
  "-tls13-variant draft23" flag to indicate compatibility with draft23
* NSS interoperability: Uses release 3.35
* PicoTLS interoperability: blocked. Doesn't seem to implement draft23
* Uses updated bogo from
  https://github.com/henrydcase/crypto-tls-bogo-shim

Goal of this PR is to rework testing script so that actual testing is
easy to extend and perform during development cycle.

* For interoperability testing I use python script and test framework,
  instead of complicated bsah scripts. Script itself is not yet perfect
  but it makes it much easier to extend tests and work with them during
  development time

* Makefile has been extended and now includes all steps needed to build
  the library and run tests. It's now possible to run any kind of tests
  without exporting environment variables.  Thanks to this change it is
  stupid-easy to run any kind of tests.

* There are 3 kinds of tests implemented in the library - unittests,
  interoperability tests and bogo. Travis has been changed and now
  dashbord will show only results for those 3 targets.

Temporarily reverts update to go1.10

Following things where added/changed:
* Builds correctly tls-tris. Previously go had a problem with
  a symbolic link resulting in not building tls-tris at all. I've
  used `rsync' instead.
* Can build for selected platform with "ARCH=platform make -f Makefile"
* Possible to build from any directory. Previously ``cd _dev; make``
  was required, it's possible to ``cd /whever/you/want; make -f /tris/Makefile``

Over time the amount of custom Go patches reduced, and tris got less
tangled to the underlying Go. Finally sever the link.

This allows more flexibility in what base Go is used (the system one),
doesn't require coordinating two repositories, and simplifies the black
magic considerably.

Make sure to use tris with Go 1.9.X.

Force boringssl client and server to use draft 22 instead of draft 18.
Other clients (tstclnt from NSS, picotls) support only draft 22.

Disable mint, it only supports draft 21.

Check SupportedVersions for the actual version and verify that the
server sets the correct SeverHello.legacy_version. Change D21 to D22.

D19 added an additional pre-extract Derive-Secret stage. D20 shortened
labels. Bump from D18 to D21 with no backwards compat option for now
since older drafts are considered undeployable.

Similar to boringssl, reuse the NSS client image for the NSS server test
against the tris client. Bump the NSS version to 3.34.1 gain support
for TLS 1.3 keylogging which is useful while debugging.

Adjust read check to fix intermittent NSS test failures:
https://github.com/cloudflare/tls-tris/issues/58

Prepare framework for testing tls-tris as client against other servers.
Currently only boringssl is implemented, but the idea is to add support
for others too (NSS, OpenSSL, picotls, tris, ...).

To test multiple certificate types, copy ecdsa.pem and rsa.pem from
tris-localserver for boringssl. The boringssl image is reused for the
server since the binaries were built anyway. Revision is bumped to
something to fix a build error and make the -loop and -www options work.

The default version (TLS 1.2) is no longer overridden with TLS 1.3 so
the server must explicitly set it.

Fixes: ("crypto/tls: allow client to pick TLS 1.3, do not enable it by default.")

This makes it easier to validate the handshake contents using Wireshark.

Use Go 1.9 (go1.9) with a patch to enable users to access the 0RTT API:

    net/http: attach TLSConnContextKey to the request Context

HEAD is currently breaking the build.