Support local installs (via `yarn add`)

[wincent]

yarn add git-cipher

Will let you run commands like this:

yarn run git-cipher init
yarn run git-cipher unlock
yarn run git-cipher add foo.txt

But clean/smudge (etc) filters won't work because git-cipher init sets them up to run:

git-cipher clean %f

ie. it assumes a global install.

So, we should support that, and teach init to instead configure things to run as:

yarn run git-cipher clean %f

(etc)

Or perhaps:

$absolute_path_to/node_modules/.bin/git-cipher clean %f

Or, teach the globally installed git-cipher to look for a local copy and delegate to that if present.

[wincent]

At the moment, toolPath() does this:

git-cipher/src/Config.mts

Lines 340 to 344 in ed5d06b

	toolPath(): string {
	return __DEV__
	? shellEscape(join(bin, 'git-cipher')) || 'git-cipher'
	: 'git-cipher';
	}

So, if you install as a submodule and use the wrapper script, __DEV__ is set, and when you run bin/git-cipher init you wind up with an absolute path in your .git/config, like this:

[filter "git-cipher"]
        required = true
        clean = /absolute/path/to/git-cipher/bin/git-cipher clean %f
        smudge = /absolute/path/to/git-cipher/bin/git-cipher smudge %f
[diff "git-cipher"]
        binary = true
        cachetextconv = true
        textconv = /absolute/path/to/git-cipher/bin/git-cipher textconv
[merge "git-cipher"]
        driver = /absolute/path/to/git-cipher/bin/git-cipher merge %O %A %B %L %P
        name = git-cipher merge driver for merging encrypted files

Likewise, init will set up a pre-commit hook for you with contents like thes:

#!/bin/sh

/absolute/path/to/git-cipher/bin/git-cipher hook

All this works, but it is fragile in the face of things like moving the repository directory after init.