feat: add `Photos.download(location)` #53

# to view logs

	name: CI

	on:
	push:
	branches:
	- main
	pull_request:

	jobs:
	build:
	runs-on: ubuntu-20.04

	services:
	mockserver:
	image: mockserver/mockserver
	ports:
	- 1080:1080

	steps:
	- uses: actions/checkout@v1

	- uses: dart-lang/setup-dart@v1
	with:
	sdk: stable

	- name: Install dependencies
	run: dart pub get

	- name: Run tests
	run: dart pub run test

	- name: Run example
	run: dart example/lib/main.dart
	env:
	UNSPLASH_ACCESS_KEY: ${{ secrets.UNSPLASH_ACCESS_KEY }}
	UNSPLASH_SECRET_KEY: ${{ secrets.UNSPLASH_SECRET_KEY }}

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