Syntax for options and dependencies

[rniii]

Currently passing options via environment variables works, but it's not exactly the nicest thing

As a main goal, the syntax should be immediately obvious to someone who doesn't use maid, and I also would like it to not have english words (e.g. like Run task ... before this). This is probably the point where this'll be different than the original repo, plus alternatives like mask

Syntax for options

I propose this:

### install

Installs project onto `$dstdir`

```sh
foo ... "$dstdir/bar"
```

It already kind of works, since the shell is run with -eu, not setting $dstdir before running maid install would crash. However it'd be nice if this was detected, and you could simply run maid install somedir (or maid install dstdir=somedir)

Syntax for dependencies

Not really sure. You can already simply run maid inside other tasks, but this is clumsy for non-shell tasks. File dependencies (like traditional make tasks) would also be pretty useful (I'm personally tired of using Rakefiles)

[rniii]

For file deps it might be worth looking into egoist/maid#9. Maybe I'll support this syntax but I'd like a nice non-english alternative