Update jline dependency

Update to more recent version: jline: 1.0 -> 2.6+ (this has a dependency on jansi, so it makes sense to also update that to 1.8)

Involves (thanks for input from Jason Dillon): the api changes from 1->2 are mostly package name changes, some generic signatures and some spelling fixes (e.g. completor -> completer) etc.

Possible specifics (some may become irrelevant depending on the approach taken):

• Terminal is an intf now; use TerminalFactory to get instances of a Terminal
• Terminal.getTerminalWidth() is now simply Terminal.getWidth()
• ConsoleReader is now in jline.console
• history functionality is now in jline.console.history, History is an intf now
• completer functionality is now in jline.console.completer
• SimpleCompletor (in groovysh) is about the same as StringsCompleter

This will be a breaking change (albeit to a mostly internal api) since org.codehaus.groovy.tools.shell.Command has a method Completor getCompletor() which should probably be renamed to getCompleter() and will return a class in a different package.