JRFC 37 - Dependencies on Github

# Adding Dependencies to Github Issues

This is an old idea, many people have had it. I'm just laying out here as a point for discussion, so that we can build it.
## Desires
- I would like to be able to link github issues to each other with a "depends on" relationship.
- I want graphs like this:
- It wont happen on github core: https://github.com/isaacs/github/issues/210
- I want gantt charts
## Proposal
### 1. Parse Dependencies from Comments

We can parse comments in an issue and detect text like:

```
Depends on https://github.com/ipfs/go-ipfs/issues/100
```

To make the dependency graph explicit. Then we can create a tool (or a site like waffle.io) that crawls a repo's issues.
### 2. Put dependencies on ipfs

Take the crawled dependencies and put them on IPFS (dag base)
### 3. Generate visual graphs

Use tools like graphviz to visualize dependency graphs.
### 4. Webapp showing deps

We can make a webapp that shows dependency graphs for:
- a single gtihub issue
- a selcted set of github issues (github search)
- a github label
- a github milestone
- a github repo
- a github org

(Note that if we implement support based on running github searches, we get most of these for free.)
### Other Considerations
- Tool/site should be able to crawl a set of orgs (all repos), or a set of repos.
- Tool should show what's done (green), ready to be worked on (yellow), what's blocked by a dependency (red), etc. (See how other tools figure out the state / info to show)
- Security: option to only look at the main issue comment/post (first, top). This way people can't troll an issue adding bogus dependencies. Requires admin powers to edit the main issue post and add the dependencies there.