Prototyping improved lazy series
Propagate builders in frame operations, print frame using address sub-range
Add virtual frame, fix printing
Return mappings as KVP (struct) and optimize sorting
Virtual frame extensions and optimizations

 * Change parameters of GetRange (to match common pattern)
 * Add 'Init' operation to vector builder and use it to make
   'frame.Rows' optionally a lazy operation (for virtual frames)
 * Optimize slicing on 'frame.Rows.[a .. b]' and add 'GetSubrange'
   operation to the frame
 * Support laziness on the 'Select' series operation
 * Materialize series using the materialization operation
 * Support lots of things on virtual frames
Add virtual ordered index

This lets us create a series that is indexed by DateTimeOffset, but
uses a virtual vector storing the keys under the cover.
Two-way map operation, work on search in vector, support more virtual operations
Generalize ranges and support search by value on virtual vectors
WIP: Scan based filtering
Fix naming, make test compile
Merge changes
FilterRowsBy works on series projected from Rows
Merge branch 'bigdeedle' of github.com:tpetricek/Deedle into bigdeedle
Remove obsolete abstractions
Revert unnecessary changes in DelayedSeries and project
Simplify vector combine behaviour (#205) and hange how Rows work

To make big deedle work correctly, I had to change how `frame.Rows` work
- the result has to be built from the source vectors, rather than creating
it from scratch as an array (that way, we BlockStore implementation can
correctly propagate the IRowIndex of the source vectors).

That change made accessing `frame.Rows` slower, because it was essentially
constructing the entire series of series (in ordinary deedle).

This commit simplifies how vectors are combined (removing `Combine` and
leaving just `CombineN` as per #205) and it adds an optimization for creating
`Rows` - when the transformation is combining of vectors, we handle it in
a special way (in `ArrayVectorBuilder`) and return a virtual "row reader"
vector. This still has more overhead than the original small-deedle version,
but only by 50% or so.
Fix compile error in tests
Fix tests, do not use CombinedRelocations for binary operators (workaround for #252)
Add FilterRowsBy extension method
Optimize merging - use CombinedRelocations