Add identifiers high-lighting

We now make use of the more specific '_type_identifier' and
'_field_identifier' rules!

queries/highlights.scm

@@ -1,5 +1,9 @@
 ; Misc {{{
 (comment) @comment
+
+(type_identifier) @type
+(field_identifier) @property
+(identifier) @variable
 ; }}}
 
 ; Keywords {{{

test/highlight/identifiers.tig

@@ -0,0 +1,29 @@
+type int = int
+/*   ^ variable */
+/*         ^ type */
+
+type int_array = array of int
+/*                        ^ type */
+
+type record = {a: int, b: string}
+/*             ^ property */
+/*                ^ type */
+/*                     ^ property */
+/*                        ^ type */
+
+var record := record {a = 12, b = "27"}
+/*  ^ variable */
+/*            ^ type */
+/*                    ^ property */
+/*                            ^ property */
+
+var array := int_array[12] of 27;
+/*  ^ variable */
+/*           ^ type */
+
+primitive func(a: int, b: string) : array
+/*             ^ variable */
+/*                ^ type */
+/*                     ^ variable */
+/*                        ^ type */
+/*                                  ^ type */