travis-ci: add osx builds

Fix MacOS building (master branch)

Fixes #122

Не учитывается значение carry

initial cirrus-ci support

test_tls: use socketpair instead of network connection

May fix build on Cirrus-CI, issue #134.

Fix compilation on FreeBSD

Otherwise `struct sockaddr_in` is undefined for test_tls.

Reported in #123 by f-andrey.

test_digest and alignment fix for Streebog

Some architectures in some circumstances do not allow unaligned
memory access (such as ARM, MIPS) triggering SIGBUS. This patch
very crudely fixes this issue.

The issue is found and original fix is proposed by Eric Biggers:

  https://patchwork.kernel.org/patch/10878865/

Especially test alginment problems on MIPSel.

travis-ci: switch to xenial

test_tls: simple TLS connection testing

Generate cert for every parameter, set it up on s_server, connect
s_client, and transfer 1M of data to both directions.

Migrate test framework to Test2

At least Fedora 30 will have no Test::More anymore. Test::More is
deprecated, as well as Test::Stream and Test2 is a recommended
replacement.

Luckily, gost-engine's use of Test::More is limited to functions which
are compatible with implementations in Test2, so only module import and
test plan announcement need to change.

Also, on Fedora 29 perl 5.28 is very picky on undefined variables.

tests: Load just built engine from the output directory

Define ENGINE_DIR for all binary tests. Instead of auto-loading engine
using `example.conf' load it directly from the OUTPUT_DIRECTORY for
curves tests.

cmake: benchmark/sign - link with rt for clock_gettime when needed

Test if clock_gettime() requires linking with -lrt and link sign
benchmark with rt if needed. clock_gettime() requires -lrt only for
glibc versions before 2.17.

travis: Enable ASan build

Fix leaks in tests

In preparation for memory leak detector fix them in the tests.