17.2.0

• Added SingletonType, which serializes a single value, e.g. a string literal. It is a more efficient encoding of an EnumType with only one possible value. See the documentation for more information.
• Added TypeScript __promisify__() declarations to I/O functions so they can now be used with util.promisify() in TypeScript code
• Rewrote README to simplify examples and clarify explanations
• Fixed tests so Node 8 is supported in addition to 9 and 10
• SHA256 is now implemented in WebAssembly, so computing type signatures will run faster on platforms that support WebAssembly (e.g. Chrome and Node.js 8+)
• Refactored I/O functions to avoid unnecessary ArrayBuffer slicing
• Lazy computation of EnumType.valueIndices map
• Updated dev dependencies
• A lot of refactoring to make the code more concise