Slice Highlighter 3.0.0

What's Changed

• Added full highlighting support for Slice's new syntax, written in conjunction with ZeroC's latest product IceRPC.
• Removed highlighting support for candidate features that we decided not to implement in Ice.
  See 6879191 for a list of these changes.

The highlighter determines which syntax is being used based on file extension.
.ice files continue using the same syntax they always have, but now .slice files can be detected and highlighted correctly.

Full Changelog: v2.0.2...v3.0.0