SemanticVersion missing equals/not equals operator, prerelease sorted wrong

Current behaviour
```cake
new SemanticVersion(1,0,0) == new SemanticVersion(1,0,0) == false
new SemanticVersion(1,0,0) > new SemanticVersion(1,0,0, "rc0001") == false
```

Expected behaviour
```cake
new SemanticVersion(1,0,0) == new SemanticVersion(1,0,0) == true
new SemanticVersion(1,0,0) > new SemanticVersion(1,0,0, "rc0001") == true
```

I'll send a pr shortly to address this.