Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
Unvendor distutils. Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
# http://stackoverflow.com/questions/20799403/improving-performance-of-cronbach-alpha-code-python-numpy
# pythran export cronbach(float [][])
# setup: import numpy as np ; N = 600 ; items = np.random.rand(N,N)
# run: cronbach(items)


def cronbach(itemscores):
    itemvars = itemscores.var(axis=1, ddof=1)
    tscores = itemscores.sum(axis=0)
    nitems = len(itemscores)
    return nitems / (nitems - 1) * (1 - itemvars.sum() / tscores.var(ddof=1))

# http://stackoverflow.com/questions/20799403/improving-performance-of-cronbach-alpha-code-python-numpy
# pythran export cronbach(float [][])
# setup: import numpy as np ; N = 600 ; items = np.random.rand(N,N)
# run: cronbach(items)


def cronbach(itemscores):
    itemvars = itemscores.var(axis=1, ddof=1)
    tscores = itemscores.sum(axis=0)
    nitems = len(itemscores)
    return nitems / (nitems - 1) * (1 - itemvars.sum() / tscores.var(ddof=1))
