[#11] Add a system for scripts to add help and the bot to retrieve and display it.

Resolves #11

- Adds bot.help API that can be used to add and get specific help text, and a summary option to retrieve a list of all registered help texts.
- Adds a script that interfaces with the bot.help API in order to allow for display of help message by the bot itself.
- Provides basic documentation for adding  help text to your own scrips.

Example:

```
<@eojthebrave> joebot: help?
<joebot> Detailed information is available with "BOTNAME: help <feature>?" where <feature> is one of: factoids, help
<@eojthebrave> joebot: help?
<joebot> Detailed information is available with "BOTNAME: help <feature>?" where <feature> is one of: factoids, help
<@eojthebrave> joebot: help factoids?
<joebot> Set factoids with "BOTNAME: Metal is great." or  "BOTNAME: cats are furry." or "BOTNAME: ping is <reply>WHAT?!". You can use the !who placeholder, it will be replaced with the nick of the user performing the query. Retrieve with "Robots?" or "BOTNAME: cheer!" Forget with "BOTNAME: delete factoid ping".
```
A common pattern I've seen if we only need one of these instantiated is to have `new Help();` be in the module exports itself.

In help.js:
```js
function Help(bot) {
  ...
}
module.exports = new Help();
```

Then, to use it:
```js
var myHelp = require('./src/help.js');
```