Add `~` as user home support for import path

**Is your feature request related to a problem? Please describe.**

`import * from "~/.amber/helpers/git.ab"`

**Describe the solution you'd like**

Load amber module from user home.

**Describe alternatives you've considered**

The following code is some complicated.

```
import { env_var_get } from "std/env"
const home = trust env_var_get("HOME")
import { history } from "{home}/.amber/helper/git.ab"
```