Deprecate eval and include, and recommend alternatives

[fonsp]

eval and include both produce confusing behaviour. I don't think they can be easily fixed without a major rewrite, but the alternatives are relatively painless!

The alternative to eval(expr) is Core.eval(Main, expr) or better yet:

🏠 = Module()

Core.eval(🏠, expr)

because this avoids an implicit state in most cases.

The alternative to include(path) is still WIP, but it will look like #115 (comment)

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Deprecating these two essentially means that your code is running in a baremodule (with using Base) instead of a module. Coincidence?