Mark up projects with metadata

[SallyMcGrath]

The projects are already in readmes, which is helpful. In order to drive the new front end, we need them to be revised in the following ways;

1. Mark up learning objectives with the custom code fence objectives eg

```objectives
1. Add three backticks
2. Write the string `objectives`
3. Write an ordered list of learning objectives
4. Close with three backticks

2. Add all the additional metadata at the head of the document. Put this in comments to hide it from the GH front end.

<!--
+++
title="Project Name"
description="A one-liner please"
time=1080
themes=['state', 'sharding', 'scaling']
prerequisites=['memcached-clusters']
+++
--->

The primers will need an extra step,

[SallyMcGrath]

@illicitonion Here's some stuff you or anyone could usefully get on with and I will build everything just assuming this stuff exists