Add another rule (candidates that appear in a single cell)
Add function block-for-cell, to remove silly candidates
Add a test selector to run certain tests more easily
Trivial formatting fixes
Add some example boards
Clean-up candidates after creating/updating the board

When creating the board, or when updating the board with new final
numbers, clean-up the candidates so they don't contain those final
numbers in the appropriate rows, columns or blocks.
Count steps a bit better
Place candidates in an easier-to-scan layout
Rename "remove-doubles" rule to the more proper "naked-pairs"
Add candidate-lines rule

Create several functions to make the candidate-lines rule (and
potentially all others) much more readable.
First X-Wing strategy implementation
Fix how the progression of the solution gets printed
Show the changes each rule makes
Add a link to the next step
Skip any steps that don't make changes
Small refactoring to use the support functions a bit more
Improve a bit the HTML output

* Add a name to every rule, and show it in every step
* Show what the last step is
* Drop "indexed" function, not needed anymore
Improve a bit the console output