Initial alpha release of Open PowerShell

Supports Windows, OS X, and Ubuntu 14.04. The Linux package includes a patched
copy of CoreCLR to address a bug that's not quite made it to NuGet packages.

On OS X, install by double-clicking the `.pkg` file and following the prompts.

On Ubuntu, install the dependencies with `sudo apt-get install libunwind8
libicu52`, then install the `.deb` file with `sudo dpkg -i`.

A symlink to the `powershell` executable will be placed in `/usr/local/bin`, while PowerShell and its runtime will be placed in `/usr/local/share/powershell`.

PowerShell will load modules in `/usr/local/share/powershell/Modules`, and will
source `/usr/local/share/powershell/PSL_profile.ps1`. A user profile placed at
`~/.powershell/profile.ps1` will also be sourced.

Windows packages are not yet supported.
