docs: update specifications

[javier-godoy]

Summary

• Section 3.3: removed the four unimplemented convenience methods (setDateFormat, setDateTimeFormat, setNumberFormat, setBooleanLabels); added setNullRepresentation, setRendererFactory, and as(Class<S>) to match the actual API.
• Section 3.3 usage example: replaced setDateFormat/setBooleanLabels calls with as(…).setFormatter(…) and as(…).setRendererFactory(LocalDateRenderers.of(…)).
• Section 7 complete example: same substitution.

Rationale for spec changes

An earlier design of EasyColumn included type-specific convenience setters: setDateFormat, setDateTimeFormat, setNumberFormat, and setBooleanLabels. These were removed from the spec as a design decision. The problem is that these methods cannot be made type-safe without first narrowing V. Placed on EasyColumn<T, V> for all V, they allow:

  easyGrid.getColumn("active")      // EasyColumn<Person, Boolean>
      .setDateFormat("dd/MM/yyyy"); // compiles — silently wrong at render time

setRendererFactory(RendererFactory<T, V>) avoids this entirely. LocalDateRenderers.of("dd/MM/yyyy") produces a RendererFactory<T, LocalDate>, so assigning it to an EasyColumn<T, Boolean> is a compile error. The as(Class<S>) method narrows V explicitly before the call, making the type constraint visible at the call site:

  easyGrid.getColumn("birthDate")            // EasyColumn<T,?>
      .as(LocalDate.class)                              // V narrowed to LocalDate
      .setRendererFactory(LocalDateRenderers.of("dd/MM/yyyy")); // type-checked

The renderer utility classes (LocalDateRenderers, LocalDateTimeRenderers, NumberRenderers) provide the same named, discoverable entry points that the convenience setters would have offered.

[mlopezFC]

LGTM