Fix TextMate regex (#137)

* tm syntax: remove verification behind command
It surely has been useful in early stage of the syntax
but it's seems to have no impact now

* tm syntax: add variable fields in "variables"
get rid of non-fixed text width lookbehind, incompatible with PCRE regex

* tm syntax: fix variables regex
variable can have 0 or more fields

Author: glcraft

syntaxes/nushell.tmLanguage.json

@@ -119,7 +119,7 @@
       "name": "variable.parameter.nushell"
     },
     "variables": {
-      "match": "(\\$[a-zA-Z0-9_]+)",
+      "match": "(\\$[a-zA-Z0-9_]+)((?:\\.(?:[\\w-]+|\"[\\w\\- ]+\"))*)",
       "captures": {
         "1": {
           "patterns": [
@@ -129,11 +129,14 @@
               "name": "variable.other.nushell"
             }
           ]
+        },
+        "2": {
+          "name": "variable.other.nushell"
         }
       }
     },
     "variable-fields": {
-      "match": "(?<=\\)|\\}|\\]|\\$\\w+)(?:\\.(?:[\\w-]+|\"[\\w\\- ]+\"))+",
+      "match": "(?<=\\)|\\}|\\])(?:\\.(?:[\\w-]+|\"[\\w\\- ]+\"))+",
       "name": "variable.other.nushell"
     },
     "internal-variables": {
@@ -520,7 +523,7 @@
     },
 
     "command": {
-      "begin": "(?<!\\w)(?:(\\^)|(?![0-9]|(?<=\\)|\\}|\\]|\\$\\w+)\\.))([\\w.!]+(?:(?: (?!-)[\\w\\-.!]+(?:(?= |\\))|$)|[\\w\\-.!]+))*|(?<=\\^)\\$?(?:\"[^\"]+\"|'[^']+'))",
+      "begin": "(?<!\\w)(?:(\\^)|(?![0-9]|\\$))([\\w.!]+(?:(?: (?!-)[\\w\\-.!]+(?:(?= |\\))|$)|[\\w\\-.!]+))*|(?<=\\^)\\$?(?:\"[^\"]+\"|'[^']+'))",
       "beginCaptures": {
         "1": { "name": "keyword.operator.nushell" },
         "2": {