Editor integration for Piglet. Currently contains:

• piglet-mode, a major mode based on tree-sitter
• pdp, a Piglet Dev Protocol server implementation, for interactive eval

The package is called piglet-emacs for lack of a better name.

• piglet-mode is too reductive, it's more than just the mode
• piglet is a misnomer, you're not installing the language
• We already called the repo that

You need Emacs 29 with tree-sitter support. It may seem like some tree-sitter functions are available even if support isn't compiled in. On debian/ubuntu systems you need the package libtree-sitter0, and then compile emacs with ./configure --with-tree-sitter.