frontend: Add handling for comments

This commit introduces a comment token which is to be ignored by the
parser.

Signed-off-by: Ian Moffett <ian@mirocom.org>

frontend/parser.c

@@ -38,6 +38,7 @@ static const char *toktab[] = {
     [TT_NAME]       = symtok("name"),
     [TT_NEWLINE]    = symtok("newline"),
     [TT_SHELLBLOCK] = symtok("shellblock"),
+    [TT_COMMENT]    = symtok("comment"),
     [TT_CC]         = qtok(".cc"),
     [TT_LD]         = qtok(".ld"),
     [TT_COLON]      = qtok(":")