fix: correctly highlight text verbatim (#28)

* fix: correctly highlight text verbatim

* fix: allow text verbatim to start with vertical line

correctly handle following:

```jsonnet
|||
 |
 ||
 |||
|||
```

* fix: correctly parse end of text verbatim

Author: mochja

language/jsonnet.tmLanguage.json

@@ -132,7 +132,7 @@
                     "include": "#double-quoted-strings"
                 },
                 {
-                    "include": "#triple-quoted-strings"
+                    "include": "#block-text-verbatim"
                 },
                 {
                     "include": "#builtin-functions"
@@ -232,12 +232,19 @@
                 }
             ]
         },
-        "triple-quoted-strings": {
+        "block-text-verbatim": {
             "patterns": [
                 {
-                    "begin": "\\|\\|\\|",
-                    "end": "\\|\\|\\|",
-                    "name": "string.quoted.triple.jsonnet"
+                    "begin": "(?:\\|\\|\\|)(?:\\s*$)",
+                    "end": "^\\s*\\|\\|\\|",
+                    "name": "keyword.other.jsonnet",
+                    "patterns": [
+                        {
+                            "begin": "^([ \t]+)(?! |\t)",
+                            "end": "^(?!\\1|\\s*$)",
+                            "name": "string.unquoted.block.jsonnet"
+                        }
+                    ]
                 }
             ]
         }