Organize F# language guide toc/index, add F# scenarios

[dsyme]

@KathleenDollard and I are working to reduce the perceived complexity of the F# docs.

Primary problems addressed:

1. The TOC for language reference is one long list of 80 entries without organization
2. The front page is sparse and awkward ("F# tutorials" and "F# tools" are very sparse)
3. F# scenarios of machine learning and web programming are not mentioned or linked

• The TOC is now simpler and more compelling with the following entries
  • What is F#
  • Get started
  • Language guide
  • Tutorials
  • Tools
  • What's new
  • F# Style guide
  • F# for machine learning
  • F# for web development
  • F# on Azure
• The front page now follows the C# structure with
  • "F# language reference"
  • "F# fundamentals"
  • "F# tools"
  • "F# in practice"
    To do this we merges "F# library reference" into "F# language reference" and "F# style guide" with "F# in practice"
• "F# in practice" has "F# machine learning" and "F# web programming" The pages reference ML.NET, Azure docs and some stable external F# community resources and guides
• The TOC for the language guide has beeen organised to just have 17 top entries (down from 80!!) in a coherent way that follows a typical F# learning sequence (we can iterate further on this after this PR)
  • Literals
  • Strings
  • Values and functions
  • Loops and conditionals
  • Pattern matching
  • Exception handling
  • Types and inference
  • Tuples, lists, collections, options
  • Records
  • Discriminated unions
  • Objects
  • Async, tasks and queries
  • Structs
  • .NET Interoperability
  • Organizing code
  • Reflection and quotations
  • Reference (compiler options etc.)
• Rename the "language reference" to "language guide". In reality the F# 2.0 material is a "language reference" while the rest has been written in the style of a "language guide" and overall I feel the latter name is now more appropriate since this is the primary readable language documentation we're providing in the menus.
• Trim some sections from "What's New"

[dsyme]

This is ready. It's a good update to the F# docs and would be great to have up in time for .NET 6 release

[gewarren]

This will be much better, thanks. Also, I ran a tool and it looks like these files are orphaned - i.e. not linked from the TOC:

docs\fsharp\language-reference\verbose-syntax.md
docs\fsharp\tutorials\using-functions.md
docs\fsharp\using-fsharp-on-azure\blob-storage.md
docs\fsharp\using-fsharp-on-azure\file-storage.md
docs\fsharp\using-fsharp-on-azure\queue-storage.md
docs\fsharp\using-fsharp-on-azure\table-storage.md

[dsyme]

Regarding "runtime" v "run time" v "run-time", the current .NET docs are inconsistent

• 547 "run-time"
• 208 "at runtime"
• 555 "run time"

I'll add a separate issue about that to get uniformity over all the docs

[dsyme]

Also, I ran a tool and it looks like these files are orphaned - i.e. not linked from the TOC:

This should now be fixed

I think this is ready once green

[dsyme]

@gewarren I rejigged the F# on Azure section. The "index.md" there is not so useful, it's a big swathe of "other" services, so I split out the two most important uses of F# (deployment/management of Azure resources, and Apache spark).

This meant I had to change the top panel link in docs/index.yml under "Cloud" so I took the chance to also put corresponding F# links under "Web and "Machine Learning", to the scenario pages, which seems to make things consistent now

[gewarren]

LGTM

[dsyme]

Thank you @gewarren!