bump version to 0.3
add d3 v3.4.11
add frontend development environment
port all.css to Stylus format
ignored generated css/js
use generated css
call frontend dev tools to rebuild all at release

Explicitly, `gulp release` will be called so Node.js environment is
required, but that's only the case for new version release.

Close #11
add clean task to remove all generated CSS/JS
add skip option and chain with install/develop

Now user can either

    python setup.py install
    pip install git+https://github.com/BioCloud-TW/ngcloud.git@master

    python setup.py develop
    pip install -e .[all]

All properly detected. Or one can explicitly call

    python setup.py build_frontend [--skip-if-exist]

To make sure generated CSS/JSs exist
update instruction for development build

Remove outdated methods for installation
tweak readme
Remove usage of pathlib during installation

close #12
fix npm installation instruction
fix gulp.cmd not found on Windows
fix build_frontend not calling gulp release
update frontend dev related doc
tweak doc
no pathlib needed during installation
update changlog
add result stage root detection