Implement WASI and wasmedge_process host functions on Windows

WebAssembly has become extremely popular among the developer community lately. It offers near native performance in a browser and is meant to not be a hand written language but to be the compilation target of source languages like C, C++, Rust etc. It provides a way to run code written in multiple languages on the web at near-native speed, with client apps running on the web that previously couldn't have done so. It, being a new language , does not enjoy wide support across platforms. The prospect of having a unified interface for web developers has long been elusive. It has the potential to provide the basis on which many apps can be built and deployed for a huge range of devices from IoT devices to fully fledged servers. But to enable developers to use it we need a WASI runtime ecosystem to support them. WasmEdge is one such project that aims to bring WebAssembly to the edge. To provide a unified interface accross multiple platforms, a interface between WasmEdge and the host operating system has to be built. This interface is specific to the platform on which the runtime is deployed and has to be built individually and specifically for each platform bearing in mind the features available. The native API provided by the OS should be used to implement many of the common operations like file manipulation, IO etc. These 'host functions' are crucial for the project to succeed and have been defined in WASI - the Web Assembly System Interface which is a modular collection of standardised APIs Currently, host specific functions have not been implemented in WasmEdge, for the windows platform. These functions are supposed to be implemented using the Win32 API and have to go rigorous testing before being deployed.