Add loader registry

[ibgreen]

A lot of doc changes creating noise so I copy the essential doc here

Loader Registry

The loader registry allows applications to cherry-pick which loaders to include in their application bundle by importing just the loaders they need and registering them during initialization.

Applications can then make all those imported loaders available (via format autodetection) to all subsequent parseFile and loadFile calls, without those calls having to specify which loaders to use.

Usage

Initialization imports and registers loaders:

import {registerLoaders} from '@loaders.gl/core';
import {CSVLoader} from '@loaders.gl/csv';

registerLoaders(CSVLoader);

Some other file that needs to load CSV:

import {loadFile} from '@loaders.gl/core';

// The pre-registered SVLoader gets auto selected based on file extension...
const data = await loadFile('data.csv');

Functions

registerLoaders(loaders : Object | Object[])

Registers one or more loader objects to a global loader object registry, these loaders will be used if no loader object is supplied to parseFile and loadFile.

• loaders - can be a single loader or an array of loaders. The specified loaders will be added to any previously registered loaders.

[coveralls]

Coverage increased (+0.04%) to 26.93% when pulling 26b6974 on ib/register-loaders into 63a4765 on master.