Add build script and nuget pack

[zdjohn]

I have created a fork branch: https://github.com/zdjohn/amazon-kinesis-client-net/tree/cake
it contains following changes:

1. separating the unit test into a separate test project (Split out the Unit tests into a separate project #7)
2. added initial nuget config file under ClientLib (NuGet Package #3)
3. added build script using cake.
4. added appveyor CI (i am happy to transfer the project)

How to use:
run ./build.ps1

What's included in build

1. solution msbuild
2. run unit test
3. download all depending jars from maven, using bootstrap
4. generating nuget package for ClientLibrary and include downloaded jars as part of Nuget content)

What's missing

1. Publish to nuget (I can use my own account to publish, however, if there is a centralized aws account in nuget would be more proper)
2. Update CI e.g. appveyor (optional) to publish nuget package with versioning.
3. we may need to add tagging in current repo.
4. add install.ps1 to nuget package, enable variables settings update in kcl.properties after nuget install

Please let me know your thoughts. I will create PR afterwards