Add the "evscript" package

[ISSOtm]

• [x] I'm the package's author and/or maintainer.
• [x] I have have read the docs.
• [x] I have tagged a release with a semver version number.
• [x] My package repo has a description and a README describing what it's for and how to use it.
• [x] My package doesn't add context menu entries. *
• [x] My package doesn't add key bindings. **
• [x] Any commands are available via the command palette. (None.)
• [x] Preferences and keybindings (if any) are listed in the menu and the command palette, and open in split view.
• [x] If my package is a syntax it doesn't also add a color scheme. ***
• [x] If my package is a syntax it is named after the language it supports (without suffixes like "syntax" or "highlighting").
• [x] I use .gitattributes to exclude files from the package: images, test files, sublime-project/workspace. (There are none.)

My package is a new syntax definition, with no accessories for now. (I'll add some goodies in a later release, e.g. "shell config"; but I want to move on for a while.)

There are no packages like it in Package Control. (The language is really niche.)

• [x] For bonus points also considered how the review guidelines apply to your package: https://github.com/wbond/package_control_channel/wiki#reviewing-a-package-addition