Docs, examples and tests should use feature names

[hardbyte]

Most of the docs don't show the newer/preferred way of defining a blocking schema with explicit column names. The functionality is mentioned in the tutorial, along with a single example:

https://blocklib.readthedocs.io/en/latest/tutorial/tutorial_blocking.html#Feature-Name-are-also-Supported!

As the blocking schema isn't complete (see #12), a user can't use that as a reference either.