Fix SA1512 blank line reported between single line comment and documentation comment

[Noryoko]

• Add regression tests for SA1512 (A single line comment must not be followed by a blank line) should allow blank line between single line comments and documentation comments #1130
• fixes SA1512 (A single line comment must not be followed by a blank line) should allow blank line between single line comments and documentation comments #1130

[Noryoko]

@oatkins In testing I found that classic StyleCop allows a blank line between a single line comment and a multi-line comment. Can you double check this?

[oatkins]

@Noryoko Yes. In fact the following is legal:

// Something in advance.

// Another comment.

/* 
 * And another/
 */

/// <summary>The YetMore class.</summary>
/* Multi-line comment
 * 
 */
public static class YetMore { }