add nuget .nuspec files for x86 and x64 separately

Hi Taliesins,

This is a pullrequest for a more standard nuget packaging solution for x86 and x64 version of packages. 

1. Check https://nuget.org/packages?q=x64, you could see most (almost all) packages depending on C/C++ libraries, for instance 
clrzmq, have separate x86 and x64 packages. I agree that, technically, we are able to create one nuget package for both x86 and x64, but it is not kind of the standard way, and it then needs additional tricky install scripts. So I created two separated .nuspec files for x86 and x64 package, inside each, there are only .nuspec and .dll files which are necessary, which makes it very easy to understand and to maintain.

2. For the VC++ runtime dependency, according to what zeromq does, I'd suggest not to embed the VC++ runtime inside the package. I added comments to the description of each .nuspec  file to remind user to install the correct VC++ runtime version by themselves.

3. Basically, in this commit, I created a nuget folder in the root folder, and I created separated x86 and x64 folders for each CPU target platform, inside, for instance the x64 folder, there is the .nuspec file, and there should be a lib folder (although it is not committed) containing the Noesis.Javascript.dll file for net35 and net40. The folder structure should be like below:
lib
 -net35
   -Noesis.Javascript.dll
 -net40
   -Noesis.Javascript.dll

We could easily package with the command below to do packaging:
nuget pack Noesis.Javascript.x64.nuspec