Entirely reworked text handling pipeline

This breaks the text pipeline into the following pieces:

- input parsing (split known bracketed phoneme sections out first)

- normalization (fix spacing, numbers, abbreviations, etc.)

- phonetization (do CMUdict lookup or g2p prediction)

- sequencing (convert the symbolic representation to integer
  representation)

Each "pipeline" can have a unique combination of operations for each of
these pipeline steps.

This will grow over time.

tts/pyproject.toml

@@ -0,0 +1,10 @@
+# For pytest
+
+[build-system]
+requires = ["setuptools>=42", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[tool.pytest.ini_options]
+pythonpath = [
+  "."
+]