Scalar-only accessors support; arc enabled by default

* `arc` template variable enabled by default, you can disable it by pasing `--template-var arc=false`
* Support for scalar only accessors: in User Info section of CoreData editor you should add `mogenerator.scalarOnly` key; `setPrimitveProperty:` and `primitiveProperty` methods are not implemented. This will generate code similar to following:

`Machine.h`

```objective-c
@property int32_t state;
- (int32_t)state;
- (void)setState:(int32_t)value_;
```

`Machine.m`

```objective-c
- (int32_t)state {
	[self willAccessValueForKey:@"state"];
	NSNumber *result = [self primitiveState];
	[self didAccessValueForKey:@"state"];
	return [result intValue];
}

- (void)setStateValue:(int32_t)value_ {
	[self willChangeValueForKey:@"state"];
	[self setPrimitiveState:[NSNumber numberWithInt:value_]];
	[self didChangeValueForKey:@"state"];					
}
```