Updated logo

This updates the logo to use the new F# Software Foundation logo for F#
instead of the # sign. For details, see
http://fsharp.org/foundation/logo.html
Typed access to Rows via an automatically implemented interface

Initial implementation that makes it possible to use frame rows in a more
type safe way than using just `df.Rows` (without waiting for type provider
features in the next version of F#).

This lets the user define an interface (by hand) and then fits the columns
of the frame to the members of the interface (see example in tests).
Merge pull request #282 from tpetricek/master

Update Mono version & cleans up and aggregates fixes #279 and #278
Optimize the performance of typed row access
Merge pull request #273 from ReedCopsey/master

Updated logo
Cleanup and comment typed rows access, add documentation & update F# Formatting
Support conversion to compatible property type
Remove forgotten comments
Merge pull request #285 from tpetricek/master

BigDeedle improvements (replacing columns, sorting, merging ordinally indexed)
Merge pull request #281 from tpetricek/typed

Typed access to Rows via an automatically implemented interface
Update Release Notes doc