Environments

[EverlastingBugstopper]

This PR will add the feature described in #385.

TL;DR: Wrangler users want to be able to push their same workers project to multiple places, perhaps they have a production, staging, and dev worker. This PR allows them to do so with the introduction of the --env flag and some changes to wrangler.toml. Most notably, private has been deprecated, workers_dot_dev has been added as a boolean field, and you can specify new environments with [env.foo]. To read more, please see this document.

Contains

• Adds tests for building with multiple environments
• Separate deprecated tomls in fixture directory
• parse multiple environments from wrangler.toml
• deprecate --release
• pass desired environment via --env or -e for wrangler publish from command line
• add workers_dot_dev to wrangler.toml
• define default behaviors at top of wrangler.toml and inherit throughout each environment
• renames Project to Target, the reasoning behind this is that Project seems to describe an entire codebase, when what we're really doing is passing around an object that specifies where the worker is deployed to -- seems like Target is a more suitable name.
• documentation for environments feature

Completed issues

Fixes #357, #385, #388

[ashleymichal]

one weird comment on a result ? that appears impossible to hit in this implementation so prolly is fine.

[gabbifish]

Since this is an amalgamation of smaller PRs I have already approved, reading through this didn't surface much for me to comment on. LGTM!