Blockstack provider

This is the implementation of a blockstack provider within storage stack.

$3

A provider is an abstract definition of a storage mechanism. Every provider can set, get and delete content.

You can register a provider on the application object of storagestack.
``typescript
ss.registerProvider(new BlockstackProvider());
`

Or when you want to use a pattern ...
`typescript
ss.registerProvider(new BlockstackProvider(), '*-index.json');
``

Take a look in the core library to the provider interface.