anchor.diff:   * only document author can add signatures to a document
   
   Notice that `type` and `value` could be anything, not restricted to any particular hash name or value.
  -  Which allows to store ordinary key-value pairs here. May be a "_filename=<filename bytes>_", or anything.
  +  Which allows to store ordinary key-value pairs here. May be a metadata like "_filename=<filename in ascii>_".
   
   .Example 1, with standard signatures
   |=======================================================
  
positive.code: = Toporick
  
  Toporick is an Ethereum Smart Contract for storing signatures of off-chain entities in blockchain. This
  could be a signatures of digital documents, images, PDF or any other file.
  
  The plan is to make a collection of Smart Contracts, which will be helpful for making an agreement
  based on references to the off-chain digital documents.
  
  Roadmap:
  
    1. [X] publish signatures to blockchain - Simple Signature
    2. [ ] add signatures from multiple parties
    3. [ ] verification of signatures
    4. [ ] smart agreement based on state of signatures
  
  == Simple Signature contract
  
  
negative.code: 
  Use case:
  
   * publish signatures of a downloadable file for a validation (like what we have for Ethereum client itself, published on
   official repo; now it can also be published into blockchain)
   * demonstrate proof of document existence at a point of time
  
  Notice that unlike to existing way of publishing such signatures on a website/ftp, publishing to blockchain through
     Toporick, it protects signatures from forgery. Once it published on blockchain, it stays here forever.
  
  It allows to:
  
  