Allow LogicalColumnReader to be IEnumerable<T>

[GPSnoopy]

Feature requested by user.

Currently they have to write it themselves. Not sure if we want to provide this or not (i.e. whether it's going beyond the scope of this library).

[GPSnoopy]

I'd favour a method that returns an IEnumerable from a LogicalColumnReader rather than making the reader IEnumerable.

[GPSnoopy]

foreach (var value in rowGroupReader.Column(c).LogicalReader().Enumerate())
{
    /* ... */
}

[herebebeasties]

I'd probably name that AsEnumerable() as opposed to Enumerate() to be more idiomatic.

But TBH I'm not sure why you'd bother returning a separate IEnumerable<T> like that, instead of just making LogicalColumnReader implement it. What's the reasoning there? You're already going to need to make an IEnumerator<T> which does the right thing, so why would you favour adding another layer?

[GPSnoopy]

This should be fixed in 1.4.0.2-beta3. @herebebeasties argument swayed me in favour of implementing IEnumerable<T> directly.