Closes https://github.com/pyodide/pyodide/issues/604

This creates an installable `pyodide-build` Python package that we can also upload to PyPi under https://pypi.org/project/pyodide-build/ (currently uploaded the dev version to reserve the name).

There is also the identically named `pyodide-build` CLI command which replaces `bin/pyodide`.

The short term goals is to use fewer hacks with `PATH` and `PYTHONPATH`. Long term goal make it a user facing interface for building packages instead of the Makefile.
Create an installable pyodide-build package. Closes https://github.com/pyodide/pyodide/issues/604

This creates an installable `pyodide-build` Python package that we can also upload to PyPi under https://pypi.org/project/pyodide-build/ (currently uploaded the dev version to reserve the name).

There is also the identically named `pyodide-build` CLI command which replaces `bin/pyodide`.

The short term goals is to use fewer hacks with `PATH` and `PYTHONPATH`. Long term goal make it a user facing interface for building packages instead of the Makefile.
*.a
*.o
*.pyc

*.egg-info/

__pycache__

.docker_home
.hypothesis
.idea
.mozilla
.mypy_cache/
.pytest_cache/
.vscode

build
ccache
cpython/downloads
cpython/installs
docs/_build/
emsdk/emsdk
geckodriver.log
node_modules/
packages/.artifacts
packages/*/build.log

*.a
*.o
*.pyc

*.egg-info/

__pycache__

.docker_home
.hypothesis
.idea
.mozilla
.mypy_cache/
.pytest_cache/
.vscode

build
ccache
cpython/downloads
cpython/installs
docs/_build/
emsdk/emsdk
geckodriver.log
node_modules/
packages/.artifacts
packages/*/build.log
dist/
