Allow usual capitalization of Python and JSON

[esnible]

Describe the bug
It's irritating that lang: Python produces a schema error. Similar with Jinja. It is legally important that trademarks preserve capitalization.

parser: JSON also produces a schema error.

Finally, the error message produces by PDL is The file do not respect the schema. which is ungrammatical. It should be The file does not respect the schema., or even f"The PDL file {file} does not respect the PDL schema."