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: Jinja2
  version: 2.11.3
requirements:
  run:
  - MarkupSafe
source:
  sha256: a6d58433de0ae800347cab1fa3043cebbabe8baa9d29e668f1c768cb87a333c6
  url: https://files.pythonhosted.org/packages/4f/e7/65300e6b32e69768ded990494809106f87da1d436418d5f1367ed3966fd7/Jinja2-2.11.3.tar.gz
test:
  imports:
  - jinja2

package:
  name: Jinja2
  version: 2.11.3
requirements:
  run:
  - MarkupSafe
source:
  sha256: a6d58433de0ae800347cab1fa3043cebbabe8baa9d29e668f1c768cb87a333c6
  url: https://files.pythonhosted.org/packages/4f/e7/65300e6b32e69768ded990494809106f87da1d436418d5f1367ed3966fd7/Jinja2-2.11.3.tar.gz
test:
  imports:
  - jinja2
