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/skimage/io/manage_plugins.py  2019-03-19 07:17:05.000000000 +0100
+++ b/skimage/io/manage_plugins.py	2020-12-16 12:03:52.000000000 +0100
@@ -41,7 +41,7 @@
 # the following preferences.
 preferred_plugins = {
     # Default plugins for all types (overridden by specific types below).
-    'all': ['imageio', 'pil', 'matplotlib', 'qt'],
+    'all': ['imageio', 'pil', 'matplotlib'],
     'imshow': ['matplotlib'],
     'imshow_collection': ['matplotlib']
 }

--- a/skimage/io/manage_plugins.py  2019-03-19 07:17:05.000000000 +0100
+++ b/skimage/io/manage_plugins.py	2020-12-16 12:03:52.000000000 +0100
@@ -41,7 +41,7 @@
 # the following preferences.
 preferred_plugins = {
     # Default plugins for all types (overridden by specific types below).
-    'all': ['imageio', 'pil', 'matplotlib', 'qt'],
+    'all': ['imageio', 'pil', 'matplotlib'],
     'imshow': ['matplotlib'],
     'imshow_collection': ['matplotlib']
 }
