Add libyaml-cpp-dev to Ubuntu/Debian installation
Add libyaml-cpp-dev to Ubuntu/Debian installation

Otherwise I received the following error:

```
Running PyYAML-3.12/setup.py -q bdist_egg --dist-dir /tmp/easy_install-jnm6__7s/PyYAML-3.12/egg-dist-tmp-uocwz8if
build/temp.linux-x86_64-3.5/check_libyaml.c:2:18: fatal error: yaml.h: No such file or directory
compilation terminated.
```
ethereum/pyethereum,ethereum/pyethereum