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).
Update Mono version & cleans up and aggregates fixes #279 and #278

Aside from changing the Travis config file, this incorporates the
fix from @dsyme (#279) and then it makes the documentation tests
pass - not quite sure why this works though (see #280).
Force loading of FSharp.Data to fix docs on Mono
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
Support adding/replacing columns with same-indexed series in BigDeedle

In general, we do not (yet?) support joins on BigDeedle frames and series.
But if the newly added (joined) frame or series has the same index, then
this should work. But - the index might not even support "GetRange" (which
is normally called before testing equality), so we first check if they are
the same object (which is a useful optimization anyway).

In the future, it would make sense to have some mechanism for testing
which operations are supported (so that we do not try calling
"restrict" if it is not supported). But for now, equality test should do.
Allow sorting of an already sorted virtual frame/series (#284)

Currently, the abstraction for virtual source does not provide a mechanism
for sorting things (and this sounds tricky to do), but if the frame/series
is already sorted, we do not need to throw.

Better error reporting (or deciding what is not supported) is still TODO.
Support merging on ordinally indexed virtual frames & series

To implement this, we need to represent ordinal index not as `int64 * int64`
(single range) but as `(int64 * int64) list` (a sequence of non-overlapping
rnages). The commit implements this as the `Ranges` module.

There was also a bug in how missing values were generated in the test suite
for big deedle, so this is fixed (with a few test fixes).
Add forgotten file...
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
Expose information about column types via frame.ColumnTypes
Add info to release notes
Add simple test for ColumnTypes