Move source from 'buildstream' to 'src/buildstream'

.coveragerc

.gitignore

MANIFEST.in

doc/Makefile

doc/source/format_project.rst

doc/source/using_config.rst

setup.cfg

setup.py

src/buildstream/__init__.py

src/buildstream/__main__.py

src/buildstream/_artifact.py

src/buildstream/_artifactcache.py

src/buildstream/_artifactelement.py

src/buildstream/_basecache.py

src/buildstream/_cachekey.py

src/buildstream/_cas/__init__.py

src/buildstream/_cas/cascache.py

src/buildstream/_cas/casremote.py

src/buildstream/_cas/casserver.py

src/buildstream/_context.py