Rework interface to mimic bcrypto

[wemeetagain]

Resolve #29
This is a somewhat major update, in that the exported AS functions have been modified, and the exported JS/TS functions have been modified.

• synchronous module loading
  • every new SHA256() is a new WebAssembly.Instance
  • static digest reuses a singleton WebAssembly.Instance, usable for most cases
• overhauled AS interface
  • INPUT_LENGTH - the length of the default input buffer
  • input - pointer to the default input buffer
  • output - pointer to the default output buffer
  • init(): void; - reset/initialize
  • update(dataPtr: usize, dataLength: i32): void; - add data to hash, referenced by pointer and length
  • final(outputPtr: usize): void; - perform final hashing, write output to outputPtr
  • digest(length: i32): void - read data from the default input buffer with the specified length, write to the default output buffer
• overhauled TS interface
  • see src/index.d.ts - interoperable with bcrypto

[mpetrunic]

forgot changelog.md