Fixed/improved version matching

 * Added 'x' as a wildcard character (in addition to '*')
 * Fixes Dynious/VersionChecker/#33

Tested using the following:

```
    @Test
    public void TestVersionMatching()
    {
        assertTrue(MatchHelper.doStringsMatch("1.7.10", "1.7.10"));
        assertTrue(MatchHelper.doStringsMatch("1.7.10", "1.7.*"));
        assertTrue(MatchHelper.doStringsMatch("1.7.*", "1.7.10"));
        assertTrue(MatchHelper.doStringsMatch("1.*", "1.7.10"));
        assertTrue(MatchHelper.doStringsMatch("1.7.10", "1.*"));
        assertTrue(MatchHelper.doStringsMatch("1.7.10", "1.7.x"));
        assertTrue(MatchHelper.doStringsMatch("1.x.x", "1.7.10"));
        assertTrue(MatchHelper.doStringsMatch("1.x.10", "1.7.x"));
        assertTrue(MatchHelper.doStringsMatch("1.x.9.10", "1.7.9.10"));
        
        assertFalse(MatchHelper.doStringsMatch("1.6.10", "1.7.x"));
        assertFalse(MatchHelper.doStringsMatch("1.x.10", "1.7.9"));
        assertFalse(MatchHelper.doStringsMatch("1.x.10", "1.7.9.10"));
        assertFalse(MatchHelper.doStringsMatch("1.*.9", "1.7.9.10"));
        assertFalse(MatchHelper.doStringsMatch("1.*.9", "1.7.9a"));
    }
```