FIXES: #2527
* define custom docker image for travis-linux builds based on
package build image
* add macos builds
* add windows builds (currently allowed to fail)
* improve build and shell scripts as required for the CI envs
* add asio timer latency workaround
* omit several manual tests from TravisCI which cause memory exhaustion
* Remove all builds except cmake gcc & clang debug.
* Time some dependency and build operations, using a custom format to avoid
interfering with other timers.
* Use Travis's "trusty" infrastructure.
* Install more dependencies via apt.
* Update boost version to 1.65.1.
* Do not run unit tests under gdb - several security features prevent
it from running correctly.
* Run test job with two processes.
