Add support for YAML config

[RaeesBhatti]

Fixes: netlify/cli#565

[DavidWells]

We for sure need yml support nice work.

I think we need to consolidate and use @netlify/config everywhere so variables etc resolve correctly https://github.com/netlify/build/tree/master/packages/config

This is also true for in the CLI https://github.com/netlify/cli/blob/7ddd543fa131c2531c5861f8bdc049cabbe6e6f3/src/utils/command.js#L36

[RaeesBhatti]

Should we implement using @netlify/config here now since we already implemented that in the CLI. Not sure how that affects this PR!

[DavidWells]

Yeah for sure. The config parsing is happening 2 places right now

1. inside cli base command https://github.com/netlify/cli/blob/master/src/utils/command.js#L39-L40
2. inside netlify/build when netlify build cli command is run
3. and this lib

The yaml/json/toml/etc is already parsed when this lib is used and the resolved object is this.netlify.config in the CLI

Perhaps this lib can use that already resolved object instead of trying to parse things again?

[DavidWells]

Is this library used anywhere else other than the CLI?

Readme says this moved? https://github.com/netlify/netlify-redirect-parser#moved-into-the-cli

[swyxio]

that readme was old. raees unmoved it. bad call to merge it in but we didnt forsee netlify build at the time