`dir` should be go away and be rolled into `src`

Having both `dir` and `src` is confusing. Only `src` should be needed and support globbing patterns as well.

**Actual**

``` powershell
task css {
    dir "css/*.css" |
        src |
        cssmin |
        dest "output/combined.css"
}
```

**Expected**

``` powershell
task css {
    src "css/*.css" |
        cssmin |
        dest "output/combined.css"
}
```
