RFC0013: renames source-metadata to project-metadata

* follows comments received on PR
** remove whitespace
** add section to Table of Contents
** Renames `source-metadata` to `project-metadata`

[#170205764]

Signed-off-by: Carlo Colombo <ccolombo@pivotal.io>

platform.md

@@ -26,6 +26,7 @@ Examples of a platform might include:
 5. [Data Format](#data-format)
    1. [order.toml (TOML)](#order.toml-(toml))
    2. [group.toml (TOML)](#group.toml-(toml))
+   3. [project-metadata.toml (TOML)](#project-metadata.toml-(toml))
 
 ## Stacks
 
@@ -62,7 +63,7 @@ The platform MUST ensure that:
 - The image config's `Label` field has the label `io.buildpacks.stack.id` set to the stack ID.
 - The image config's `Label` field has the label `io.buildpacks.stack.mixins` set to a JSON array containing mixin names for each mixin applied to the image.
 
- #### Detection phase
+#### Detection phase
 To initiate the detection phase, the platform MUST invoke the `/cnb/lifecycle/detector` executable with the user and environment defined in the build image config.
 Invoking this executable with no flags is equivalent to the following invocation including all accepted flags and their default values.
 
@@ -96,12 +97,12 @@ To initiate the export phase, the platform MUST invoke the `/cnb/lifecycle/expor
 Invoking this executable with no flags is equivalent to the following invocation including all accepted flags and their default values.
 
 ```bash
-/cnb/lifecycle/exporter -source-metadata ./source-metadata.toml
+/cnb/lifecycle/exporter -project-metadata ./project-metadata.toml
 ```
 
 Where:
 
-- `-source-metadata` MAY specify input from a `source-metadata.toml` file path as defined in the [Data Format](#data-format) section.
+- `-project-metadata` MAY specify input from a `project-metadata.toml` file path as defined in the [Data Format](#data-format) section.
 
 ### Run Image
 
@@ -139,7 +140,7 @@ The buildpacks directory MUST contain unarchived buildpacks such that:
 ## OCI Image
 The OCI image containing the compiled application is generated by the Build Image during the [Export Phase](#export-phase).
 
-If the `/cnb/lifecycle/exporter` is invoked with the optional `-source-metadata` argument, the lifecycle MUST add a `io.buildpacks.project` image config label to the new OCI image with a [value as described in the data-format](#io.buildpacks.app.source-oci-image-label-json) section.
+If the `/cnb/lifecycle/exporter` is invoked with the optional `-project-metadata` argument, the lifecycle MUST add a `io.buildpacks.project` image config label to the new OCI image. This label value is encoded JSON format of the `project-metadata.toml` contents, as described in the [data-format](#data-format) section.
 
 ## Security Considerations
 
@@ -199,7 +200,7 @@ Where:
 
 - Both `id` and `version` MUST be present for each buildpack object in a group.
 
-### source-metadata.toml (TOML)
+### project-metadata.toml (TOML)
 
 ```toml
 [source]
@@ -209,26 +210,4 @@ type = "<source type>"
 
 [source.metadata]
 
-```
-
-### io.buildpacks.project OCI Image label (JSON)
-The value of this label:
-- MUST be a string of escaped json complying with [RFC 8259](https://tools.ietf.org/html/rfc8259).
-- when unescaped, MUST comply with the following schema:
-
-```json
-{
-  "$schema": "http://json-schema.org/schema#",
-  "type": "object",
-  "properties": {
-    "source": {
-      "type": "object",
-      "properties":{
-        "type": {"type": "string"},
-        "version": {},
-        "metadata": {}
-      }
-    }
-  }
-}
 ```