STRNCMP_EQUAL - C string comparison of the first n characters

Except for macro implementation.
1. Added simple test for STRNCMP_EQUAL() macro with SimpleString.
2. Added failure tests for macro.
I've added those based on one of simple tests like this:

```
TEST(SimpleString, asCharString)
{
    SimpleString s1("hello");

    STRCMP_EQUAL("hello", s1.asCharString());
}
```