Update Licence in README File
Removed Unused Class Constants in Indexers and Experimenters

"requires_score" can be known from "required_score_type," and all other
expectations should be specified in a class' documentation. It's up to an
indexer's/experimenter's user to provide it with useful data.

Indexers:
- required_indices
- requires_score
Experimenters:
- required_indices
- required_experiments
Revise rST and Comments in Most Modules
Correct IndexedPiece and Tests for Removal of Indexer.requires_score
Add rST Files and Makefile for the vis API Documentation

Also added the _build directory to .gitignore