Change client csproj so it can be built as both x86 and x64.
Visual Studio doesn't really give us an elegant way to achieve this that I know of. Copy the client project as a new version that compiles both an x86 and x64 version, so everything is built in one pass (a 64-bit configuration would require two passes).

The new assembly gets called '...Client.x64.exe' to distinguish it from the 32-bit version (and avoid breaking existing things)
Amend nuspec file with the new client exe
I think the build target paths were wrong for the client exes
Add a 64-bit version of the process starter, rename the 32-bit version
Add a new version of the Create() method that can be used to create 64-bit as well as 32-bit child processes. Change from using default parameters to overloads so that the API is binary compatible with the old version.
Merge pull request #1 from AndrewHunterRedGate/master

Add 64-bit client