Show description for completion candidates

[snuyanzin]

Jline3 allows this.
Here it is a short example of how it could be toggled by a property
https://asciinema.org/a/251412

Also as it could be seen from the example, commands with different aliases could be aggregated together if several aliases matches for completion

[snuyanzin]

I also added another short demo on not a full screen.
https://asciinema.org/a/255980?speed=2.5&theme=solarized-dark&cols=78&rows=18

[julianhyde]

Nice! I'll tweet out that demo when the feature appears in a release.

[snuyanzin]

Command name completion merged as 6a215a1

I will check if there is a more or less simple way to support the similar behavior for variables

[snuyanzin]

I made also for schemas, tables, columns while #331

For variables there is an issue with their long descriptions that in most cases even longer that the screen's width. Simple cutting of description does not work as in most cases cut descriptions lose their sense.