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.
# Pyodide packages

This folder contains the list of packages built in pyodide.

There are two categories of packages,
 1. Those that contain a `meta.yaml` are built with the Python build system
    using `pyodide_build/buildall.py` and `pyodide_build/buildpkg.py` scripts.
 2. Those that contain a `Makefile` are build from the main `Makefile` in the
    root folder.

Packages of the second category will be migrated to use a `meta.yaml` in the
future (see [#713](https://github.com/pyodide/pyodide/issues/713)).

# Pyodide packages

This folder contains the list of packages built in pyodide.

There are two categories of packages,
 1. Those that contain a `meta.yaml` are built with the Python build system
    using `pyodide_build/buildall.py` and `pyodide_build/buildpkg.py` scripts.
 2. Those that contain a `Makefile` are build from the main `Makefile` in the
    root folder.

Packages of the second category will be migrated to use a `meta.yaml` in the
future (see [#713](https://github.com/pyodide/pyodide/issues/713)).
