Fix spelling suggestion so that it preserves capitalization

The [last commit](https://github.com/clips/pattern/commit/d1d719540f195f3028e24f4d2e536d73e9fef210) introduced a bug that caused spelling suggestions to ignore capitalization, e.g. `"The" -> ("the", 1.0)`. 

This patch reverts the last few lines of the `suggest()` method back to the old logic. A basic test was also added for this.