🐛 Move source into src/ to fix install

Installing was broken since moving to pyproject.toml, which we didn't notice because of
leftover files in build/. Fix this by using the convention of having the source files
in src/ and adjusting pyproject.toml accordingly.

Fixes gh-86. 🤞

ocrd-tool.json

@@ -1 +1 @@
-dinglehopper/ocrd-tool.json
+src/dinglehopper/ocrd-tool.json

pyproject.toml

@@ -45,8 +45,7 @@ dependencies = {file = ["requirements.txt"]}
 optional-dependencies.dev = {file = ["requirements-dev.txt"]}
 
 [tool.setuptools.packages.find]
-# This is not strictly necessary, just when junk lies around.
-where = ["dinglehopper"]
+where = ["src"]
 
 [tool.setuptools.package-data]
 dinglehopper = ["*.json", "templates/*"]