Migrate to a src/ layout

This prevents the test suite from accidentally passing
when a packaging problem is masked by `jsonpath_ng`
being importable from the root of the repository.

See #209
for a PR that demonstrates the consequences of having
`jsonpath_ng/` as a folder in the root of the repo.

In addition, this migrates from `setup.py` to `pyproject.toml`.
With this change, the project can be built with these commands:

```
pip install build
python -m build
```

Author: kurtmckee

.gitignore

@@ -10,7 +10,7 @@ __pycache__/
 # Build and test artifacts
 /README.txt
 /dist
-/*.egg-info
+*.egg-info
 parser.out
 .cache
 .coverage

pyproject.toml

@@ -1,3 +1,33 @@
+[build-system]
+requires = ["setuptools >= 77.0.3"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "jsonpath-ng"
+version = "1.8.0"
+description="A final implementation of JSONPath for Python that aims to be standard compliant, including arithmetic and binary comparison operators and providing clear AST for metaprogramming."
+authors = [
+    {name = "Tomas Aparicio", email = "tomas@aparicio.me"},
+]
+license = "Apache-2.0"
+readme = "README.rst"
+classifiers=[
+    "Development Status :: 5 - Production/Stable",
+    "Intended Audience :: Developers",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: 3.14",
+]
+
+[project.urls]
+Source = "https://github.com/h2non/jsonpath-ng"
+
+[project.scripts]
+jsonpath_ng = "jsonpath_ng.bin.jsonpath:entry_point"
+
 [tool.pytest.ini_options]
 filterwarnings = [
     # Escalate warnings to errors.