syntax: asm: highlight C-like comments (micro-editor#3696)

Different assemblers have different syntaxes for comments: ";", "#",
"!", "|", "@", "*" and finally C-like comments "//" and "/* ... */".

Micro currently highlights only ";". This is causing various problems
with broken highlighting with other types of comments (i.e. those not
recognized by micro as comments), when the text in those comments
contains special characters, causing wrong highlighting of text after
them.

On the other hand, highlighting comments like "#", "|" etc would cause
conflicts with other syntax elements, e.g. constants in ARM assembly,
preprocessor directives, arithmetic expressions etc.

So let's highlight at least C-like comments. They are quite commonly
used and they are not so likely to cause conflicts with other syntax
elements.

Author: dmaluka

runtime/syntax/asm.yaml

@@ -4,7 +4,7 @@ detect:
     filename: "\\.(S|s|asm)$"
 
 rules:
-    # This file is made for NASM assembly
+    # This file is made mainly for NASM assembly
 
     ## Instructions
     # x86
@@ -108,3 +108,16 @@ rules:
         rules:
             - todo: "(TODO|XXX|FIXME):?"
 
+    ## C-like comments (supported by some assemblers)
+
+    - comment:
+        start: "//"
+        end: "$"
+        rules:
+            - todo: "(TODO|XXX|FIXME):?"
+
+    - comment:
+        start: "/\\*"
+        end: "\\*/"
+        rules:
+            - todo: "(TODO|XXX|FIXME):?"