Add Scope::get_value_ref and get_value_mut. #1415

	name: Benchmark
	on:
	push:
	branches:
	- master
	- perf

	jobs:
	benchmark:
	name: Run Rust benchmark
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v2
	- run: rustup toolchain update nightly && rustup default nightly
	- name: Run benchmark
	run: cargo +nightly bench --features decimal,metadata,serde,debugging \| tee output.txt
	- name: Store benchmark result
	uses: rhysd/github-action-benchmark@v1
	with:
	name: Rust Benchmark
	tool: 'cargo'
	output-file-path: output.txt
	# Use personal access token instead of GITHUB_TOKEN due to https://github.community/t5/GitHub-Actions/Github-action-not-triggering-gh-pages-upon-push/td-p/26869/highlight/false
	github-token: ${{ secrets.RHAI }}
	auto-push: true
	# Show alert with commit comment on detecting possible performance regression
	alert-threshold: '200%'
	comment-on-alert: true
	fail-on-alert: true
	alert-comment-cc-users: '@schungx'

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