create rfc for @educational decorator

[gregcaporaso]

We'd want this to:

• point to a production version (and add See Also)
• inject standard warning about using efficiency of educational code version production code
• inherit docstring from production version
• confirm signature is the same between the educational and production implementations

[wasade]

I think a critical item here is how the test code is handled as I think it would be useful to exercise the API independent of the implementation. The indirection done with scikit-bio/scikit-bio#1040 probably isn't the best way to go about it, but it works for the moment. Specifically, I think we may want to do a single mixin base per method tested as opposed to having combined code (as is the case with unweighted_unifrac and weighted_unifrac). I suspect there is a common approach that can be taken with the test code which I believe would help to standardize the inclusion of different implementations of methods.

[gregcaporaso]

I agree that this is a key piece, and I agree that separating the tests out per method is a better way to go than what I did for the *unifrac tests.

[gregcaporaso]

We've decided that educational implementations are better suited for IAB, which will also simplify scikit-bio. This will be revisited in the context of IAB (gregcaporaso/An-Introduction-to-Applied-Bioinformatics#180).