Remove mentions of 'adapts' and 'implements' from examples and tutorial

[mdickinson]

This PR purges mentions of the (no-longer-extant) functions adapts and implements from the tutorial files and documentation examples.

For adapts, we've mostly gone the way of removing the offending files altogether: the adaptation story has changed enough that the old material was too far from correct to be useful. Someday it might be nice to add an adaptation tutorial back in.

For implements, we've fixed the examples to use provides instead.

Closes #437.

[rahulporuri]

LGTM