Add support for [idMember]="'key'" to specify the property used for id in the array of objects

[ishaan-puniani]

Hello,

I would like to contribute to this repo to have additional functionalities like
to have attribute [idMember]="'key'" along with [displayMember] as I am having different unique id in the array of objects
var variables = [
{
key: 0,
name: 'test0'
},
{
key: 1,
name: 'test1'
}
]

Also please document the steps/ script commands to build the component. It seems like script section is missing in the package.json

--
Thanks