Aleth 1.7.0-alpha.1

Bump version: 1.6.0-rc.1 → 1.6.0

Aleth 1.6.0-rc.1

Bump version: 1.6.0-rc.0 → 1.6.0-rc.1

Aleth 1.7.0-alpha.0

Bump version: 1.6.0-alpha.1 → 1.7.0-alpha.0

Aleth 1.6.0-rc.0

Bump version: 1.6.0-alpha.1 → 1.6.0-rc.0

cpp-build-env: Bump version to 11 to upgrade clang-8 to the release v…

…ersion

cpp-build-env:10: Install GCC 6, clang-3.8 from Debian Stretch

Aleth 1.6.0-alpha.1

Bump version: 1.6.0-alpha.0 → 1.6.0-alpha.1

cpp-build-env: Upgrade OS and compilers

- Upgrade Debian to testing.
- Upgrade default GCC to 8.
- Install GCC 7.
- Upgrade clang to 8.