Add Umbral syntax package

[hersac]

• I'm the package's author and/or maintainer.
• I have read the docs.
• I have tagged a release with a semver version number.
• My package repo has a description and a README describing what it's for and how to use it.
• My package doesn't add context menu entries.
• My package doesn't add key bindings.
• Any commands are available via the command palette. (Not applicable: syntax-only package)
• Preferences (if any) open properly in split view.
• This syntax package doesn't add a color scheme.
• I use .gitattributes to exclude non-package files.

My package is the official syntax highlighting package for the Umbral programming language.

Umbral is a general-purpose programming language created by the author of this package, with its own syntax, modules, examples, and tooling.
This package provides:

• Syntax highlighting (tmLanguage)
• File extension support for .um
• Example programs demonstrating the language
• A clean, minimal structure following Package Control guidelines

There are no other packages in Package Control that support the Umbral language.

[braver]

Looking good. Please tag your latest version, 1.1.5 still points to an older version.