Import backtrace-cpp and integrate it into our main executable

Upstream release
https://github.com/bombela/backward-cpp/archive/v1.3.tar.gz

external/backtrace-cpp/.travis.yml

@@ -0,0 +1,25 @@
+language: cpp
+compiler:
+  - gcc
+  - clang
+
+addons:
+  apt:
+    packages:
+      - valgrind
+
+install:
+  - DEPS_DIR="${TRAVIS_BUILD_DIR}/deps"
+  - mkdir ${DEPS_DIR} && cd ${DEPS_DIR}
+  - CMAKE_URL="http://www.cmake.org/files/v3.3/cmake-3.3.2-Linux-x86_64.tar.gz"
+  - mkdir cmake && travis_retry wget --no-check-certificate --quiet -O - ${CMAKE_URL} | tar --strip-components=1 -xz -C cmake
+  - export PATH=${DEPS_DIR}/cmake/bin:${PATH}
+  - pip install --user conan && export PATH=$PATH:$HOME/.local/bin
+  - cd ${TRAVIS_BUILD_DIR}
+  - mkdir build && cd build
+  - cmake .. -DBACKWARD_TESTS=ON
+  - cmake --build .
+
+script:
+  - valgrind ctest .. --verbose
+  - cd ${TRAVIS_BUILD_DIR} && conan test_package --build=outdated