adds table crates

[wookietreiber]

To explain the differences between these crates: should this be done in this useful crates section, or should this be done in subsections? The pretty-table-printing authors have made an effort of explaining the differences in their respective crates, and a summary of that might very well be included here.

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The spacing / empty newlines were just for my own sanity when looking at the actual document source. To me, it's much more readable with the additional whitespace.