docs: DocFX v2 upgrade with organized API landing page (#564)

## Summary

DocFX v2 upgrade with comprehensive documentation restructure:

### Documentation Pages
- **API Reference**: Custom landing page organized by functionality (not alphabetical)
- **NumPy Compliance & Compatibility**: Compliance goals, NEP tracking, roadmap
- **Array API Standard**: Full specification coverage, function matrices
- **Broadcasting**: Rules, shape compatibility, API reference
- **Extending Libraries**: NumSharp.Bitmap documentation

### Structure
- Custom `api/toc.yml` with categorized sidebar
- `docs/website-src/` for source, `docs/website/` for output
- Fixed README image paths

### Issue
Closes #563

Author: Nucs

README.md

@@ -1,4 +1,4 @@
-[![NumSharp](docs/images/numsharp.logo.png)](docs/images/numsharp.logo.png)
+[![NumSharp](docs/website/images/numsharp.logo.png)](docs/website/images/numsharp.logo.png)
 
 [![NuGet](https://img.shields.io/nuget/dt/NumSharp.svg)](https://www.nuget.org/packages/NumSharp)
 [![Join the chat at https://gitter.im/publiclab/publiclab](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/sci-sharp/community)
@@ -13,7 +13,7 @@ Is it difficult to translate python machine learning code into .NET? Because too
 NumSharp is the C# version of NumPy, which is as consistent as possible with the NumPy programming interface, including function names and parameter locations. By introducing the NumSharp tool library, you can easily convert from python code to C# or F# code.
 Here is a comparison code between NumSharp and NumPy (left is python, right is C#):
 
-[![comparision](docfx_project/images/python-csharp-comparision.png)](https://raw.githubusercontent.com/SciSharp/NumSharp/master/docfx_project/images/python-csharp-comparision.png)
+[![comparision](docs/website/images/python-csharp-comparision.png)](https://raw.githubusercontent.com/SciSharp/NumSharp/master/docs/website/images/python-csharp-comparision.png)
 
 ### Bold Features
 * Use of Unmanaged Memory and fast unsafe algorithms.

docs/website-src/api/.gitignore

@@ -1,5 +1,7 @@
 ###############
 #  temp file  #
 ###############
+# Generated API YAML files (except toc.yml which we customize)
 *.yml
+!toc.yml
 .manifest