Migrate to slog and core v0.3.0

• Migrate from log15 to slog (Go standard library)
• Update to core v0.3.0
• Add Apple Silicon (darwin-arm64) binary
• Fix search command panic on missing argument

Add version subcommand

Add version subcommand to prepare for homebrew formula

One click deployment with Render

• Added Viper as a configuration library
• Flushed out Render one click deployment (now deploys as a cron job + prompts user to enter necessary env vars before deploying)

Add email notification support

You can now get an email notification if a campsite is found, which is great for running the CLI tool as a daemon in the background.

➜ opencamp poll 233116 09-11-2023 09-12-2023 --interval=1m --notify=email

See https://github.com/opencamp-hq/cli#poll-campground-availability-with-email-notification for more info!

Pre-release version!

Doesn't include a notification feature yet, but you can poll recreation.gov for campground availability.