Add pre-commit hook definition with test

[dbast]

pre-commit became pretty popular as framework to combine linters / code-formatters via hooks across different languages. It can be enabled as actual git hook or just used by running pre-commit run -a. pre-commit does its own dependency management (+cashing) and installs each hook into its own isolated folder.

This adds a .pre-commit-hooks.yaml (+ doc + test), which allows other projects to run Solhint via pre-commit.

Tested it also via my solhint fork with custom test tag, see dbast/sol-press#16

pre-commit installs a hook by cloning the repo, checking out the specified git rev (=tag, branch, commit hash), parsing the .pre-commit-hooks.yaml and installing the hook (in case of node based hooks: run npm pack (produces a tarball + npm install $tarball). Installed hooks are cached based on the rev for later repeated runs.

Had to remove the prepare script in package.json as that prevents npm pack from working with a plain node install (which is used by pre-commit during isolated hook installations). prepare is afaik not the right place to run husky install.