taListItemField doesn't handle nested items

[juhaszPeterDev]

Hi!
I did my best to understand your code and found that the 'taListItemField' option doesn't handle nested objects like {a: {b: 'foo'}} and can't reach 'b' on 'a.b' path.
I found that in your /src/services/ngx-typeahead.utils.ts:109 line could be replaced from
newItem = fields.reduce((acc, cur) => `${acc}${item[cur]}`, '');
to
newItem = fields.reduce((acc, cur) => `${acc}${cur.split('.').reduce((prev, elem)=>{return prev ? prev[elem] : prev;},item)}`, '');
and this would handle nested object fields.
I would do a pull request, but I have never done it before, that's why I'm writing here. I apologize for my inability and thank you in advance for your help.

Sidenote: did you consider that taListItemField=['a','b'], object {a: 'foo', b: 'bar'} and search 'ob' can give a false positive since you string concat all fields (in this case into 'foobar')? I know that putting a space between fields doesn't eliminate all false positives but it might reduce the numbers.

[orizens]

taListItemField is considered to be used with a literal object only