Solution: add Ubuntu toolchain PPA and use GCC 6

Solution: pass -g so that valgrind/asan can print useful backtraces

Solution: import better solution from zproject and add a new autoconf
option

Solution: run make with -j5, as now the tests support it.

Solution: don't, libzmq's CI tests are not responsible for testing
libsodium stable releases. Save some time in the CI.

Solution: add a CI build run with GCC's Address Sanitizer enabled.
This compiler flag will make the unit test programs abort if it
detects errors such as out-of-bound memory access or use-after-free.

Solution: rework the bash test to avoid build failures as intended
and make it an easier one-liner

Solution: use packages on Ubuntu and brews on OSX. The packages and
the brews are always kept up to date, so it's no use to rebuild the
libsodium stable branch manually everytime.

Solution: Use travis to deploy these artifacts automatically.

The deployment is triggered by tagging on the zeromq/libzmq repository.
Of the many builds travis is checking only the default one with
libsodium and drafts disabled is used for deployment.

For now the results of `make distcheck` are deployed as well as their
md5 and sha1 hash sums. Further changes may upload a generated
Changelog as well.

Solution: do default test with DRAFT APIs enabled

Solution: run make dist-check, which will run additional tests,
including making sure that the library is installable and the
distributable tarball is buildable, along with the usual make and
make check.

Solution: simply run make VERBOSE=1 check instead of manually
checking for return value and cat'ing the log file. With VERBOSE, on
error the log file will be automatically printed.

Solution: establish a matrix of CI options. On one axis we have the
build system (autotools, cmake, android) and on the other axis we
have the encryption options (tweetnacl, libsodium or none).

Solution: build by default with tweetnacl, and add sub-build project
to test libsodium

Solution: checkout stable branch instead.
Several warnings are printed when building from the master branch,
and developers recommend using the stable branch instead.

Solution: add `--depth 1` parameter to `git clone` commands

Currently, a test fails on Travis-CI but that can not be reproduced locally.
Without the contents of the test-suite.log, this is difficult to analyze.

Solution: print test-suite.log if "make check" fails

This is based on the following answer on SO:
http://stackoverflow.com/a/32597140

ldconfig is not available on OSX, so Travis CI build fails

Solution: Add qt-android build system and add to travis-ci