v0.4.0

Added Mistral, some data structure enhancements, matching parity with tiktoken api

v0.3.2

README: pre-launch review fixes 1-5

- document the importer's verification deps (tokenizers / mistral-common /
  huggingface_hub) — the one runtime surprise a new user would hit
- quick-start import example is now the HF repo-id form, validated live
  (mistralai/Mistral-Nemo-Instruct-2407 -> verified vs mistral-common); the
  importer now prefers tekken.json over tokenizer.json when a repo has both
- SentencePiece (Gemma/T5/Llama-2) explicitly out of scope in Importing
- wheel platforms + Python floor stated in Install
- llama4 guidance works from pip: import via repo id (verified, with the
  rank-vs-merges clause); the export tool stays as the rank-truth path