Implement decoder

[mycognosist]

• Add decode() capability and helper functions
• Remove regex and lazy_static dependencies
  • Perform string manipulations using standard library features (ie. .rfind() and .strip_suffix())
• Rename ConvertedValue enum to EncodedValue
  • Rename variants to match JS expectations (Array, Buffer, Object)
  • Replace HashMap with IndexMap to preserve field order in key-value objects
• Add a test to encode and decode a heterogeneous JSON object

More tests and docs tomorrow.