fish: init

[MarcelCoding]

Add supports for the fish scripting language.

https://fishshell.com/

I am not completely sure if atom_nodes and delimiter_tokens are correct. But it seems to be working for me.

Tested using the diff of this PR: pure-fish/pure#375

[edouard-lopez]

Hello, I'm pure.fish lead dev and was looking for a Fish support PR. What a nice surprise to see you tested on it 😃
Can I help?

[MarcelCoding]

idk, I've just took the opportunity to rebase this PR. Maybe you can help with my open questions from the PR description.

[edouard-lopez]

The tree-sitter wiki mention a Fish parser https://github.com/ram02z/tree-sitter-fish

The doc on adding a parser mention how to check you set the correct values for atoms and delimiters :

difftastic/manual/src/adding_a_parser.md

Lines 68 to 70 in cc06434

	You can use `difft --dump-ts foo.json` to see the results of the
	tree-sitter parser, and `difft --dump-syntax foo.json` to confirm that
	you've set atoms and delimiters correctly.