tree-sitter: 1.18.2 -> 0.19.3

Update the grammars and add `allGrammars` derivation.
`nix-build "<nixpkgs>" -A tree-sitter.allGrammars` will create a
derivation with symlinks to all the grammars

pkgs/development/tools/parsing/tree-sitter/grammars/tree-sitter-markdown.json

@@ -0,0 +1,10 @@
+{
+  "url": "https://github.com/ikatyang/tree-sitter-markdown",
+  "rev": "5a139bed455268a06410471bf48b19d11abdd367",
+  "date": "2021-01-24T15:17:18+08:00",
+  "path": "/nix/store/125cbxcqvwyq8b7kvmg7wxjjz16s2jvw-tree-sitter-markdown",
+  "sha256": "072b4nnpymrh90y4dk18kr8l1g7m83r3gvp6v0ad9f9dnq47fgax",
+  "fetchSubmodules": false,
+  "deepClone": false,
+  "leaveDotGit": false
+}