Elvish is a scripting language and shell similar to Bash, Fish, and Zsh. This merge adds support for syntax highlighting of this scripting language.
I have added test.elv following the sample file made by the language author for the VSCode plugin.
I am very new to contributing to open source projects, so if there's anything I have to do differently or change in the syntax file, please let me know.
The tests pass, and the highlighting uses the default styles.