[RFC] Dynamically add/remove items

[krisk]

Description

Include the ability to dynamically add items to the search list.

Describe the solution you'd like

API:

• add: Adds a doc to the end of the index
• removeAt: Removes the doc at the specified index

add(doc: T): void
removeAt(idx: number): void

Examples:

const fruits = ['apple', 'oranges']
const fuse = new Fuse(fruits)

fuse.add('banana')
// -> fruits:  ['apple', 'oranges', 'banana']

fuse.removeAt(1)
// -> fruits:  ['apple', 'banana']

[krisk]

cc: @amir20, @tomas