Add option to add comments to strings via rule builder

[TadeasKucera]

We would like the withPlainString, withHexString and withRegexp accept one more parameter comment and add supplied text as a one line comment next to the string. Through Python the functions may be accessed as follows:

a = YaraRuleBuilder()
a = a.with_name("b")
a = a.with_plain_string("$s1", "hello", "COMMENT")
a = a.with_condition(of(all(), them()).get())

which would create a rule

rule b
{
  strings:
    $s1 = "hello" // COMMENT
  condition:
    all of them
}

• The new parameter comment needs to be optional.
• The comment shall be after string modifiers if present.

[jconnor0426]

Bumping this feature request. This would really help us when using Yaramod to explain why strings were added to rules