This is a partial import of rx.codeplex.com for mono.
Since rx.codeplex.com is massive and we only need partial source tree of it (and due to some checkout failure on Linux [*1]), we set up another repository for mono submodule.
This tree is hence manually imported. Though it is somewhat easy to maintain: we can cherry-pick changes only in Rx.NET in the rx.codeplex.com. Mostly we would not need to copy sources from the original treemanually, but sometimes we do when a checkout involves other directories than Rx.NET.
For every original release, we should import the updates and commit to this master, then create a branch for each release and then apply our local changes (which is minimum but required) to the branch.