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.
package:
  name: pyparsing
  version: 2.4.7
source:
  sha256: c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1
  url: https://files.pythonhosted.org/packages/c1/47/dfc9c342c9842bbe0036c7f763d2d6686bcf5eb1808ba3e170afdb282210/pyparsing-2.4.7.tar.gz
test:
  imports:
  - pyparsing

package:
  name: pyparsing
  version: 2.4.7
source:
  sha256: c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1
  url: https://files.pythonhosted.org/packages/c1/47/dfc9c342c9842bbe0036c7f763d2d6686bcf5eb1808ba3e170afdb282210/pyparsing-2.4.7.tar.gz
test:
  imports:
  - pyparsing
