Extend `getargs` with support for named arguments

The initial proposal is to support named values like so:

```
" 1  , key='2' , 3  ,'other.key'=false,5 "
```
transforms to
```
result = [ 1, "2", 3, false, 5];
result["key"] === result[1];
result["other.key"] === result[3];
```