Add buffertools and async libraries to package.json
Simplify default values for TransactionOutput
Further progress on ColoringEngine
Remove console log statements and restore inputUnitsLeft logic
Add initial progress writing tests for the ColoringEngine class
Add include async library in ColoringEngine
Use async.parallel for cleaner flow control in colorTransaction
Move async library to dependencies from devDependencies
Enable tests for ColoringEngine::getOutput
Minor cleanup, organization in ColoringEngine
Ensure issuance outputs always have output type 'isuance'
Clean up variable definitions and remove debug output
Use prevout index instead of transaction input index
Fix inline comment
Logic fixes in ColoringEngine::_computeAssetIds

- Use buffertools.equals() to compare Buffer objects. Native '=='
  and '===' always return false.
- Move the generation of the Transfer TransactionOutput object
  outside of the while loop to accurately handle cases where
  assets from multiple inputs are combined into an output.
Account for change outputs in tests for _computeAssetIds
Fix value error in reference Buffer for _computeAssetIds test
Add additional getOutput test for issuance transaction