Make it easier to specify index column & drop it when indexing

After a discussion with @hmansell and @perryvais, they finally convinced
me that `indexRows` family of operations should remove the column that
was used as the key, so this implements this (breaking) change. Using
method-based syntax, you can still call `df.IndexRows("Key", keepColumn=true)`
if you want to keep the column, but F# functions always drop the column.

Aside from that, I also added optional parameter to `ReadCsv` and to
`ofRecords`, so you can now specify index column when creating frames:

    Frame.ofRecords<DateTime>(seq, indexCol="Date")
	Frame.ReadCsv<DateTime>("file.csv", indexCol="Date")
Fix remaining tests for indexing change
Update version & build scripts & dependencies
Undo unnecessary changes in build script
Prototyping improved lazy series
Add perf test for filling missing values
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