feat(emacs): add c-sharp support

This is only initial support. Most of the features are built-in to lsp-mode. I
have added some snippets to make my life a bit easier.

There a more tweaks coming but they are general in improving the editing
experience not just targeted at c-sharp.

site-modules/core/files/emacs/snippets/csharp-mode/doc-block

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: /// <summary> ... </summary>
+# key: ///
+# --
+/// <summary>
+/// $0
+/// </summary>

site-modules/core/files/emacs/snippets/csharp-mode/inheritedoc

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: /// <inheritdoc ... />
+# key: ///i
+# --
+/// <inheritdoc${1: cref="${2:Class}"} />$0

site-modules/core/files/emacs/snippets/csharp-mode/pbsd

@@ -0,0 +1,13 @@
+# -*- mode: snippet -*-
+# name: Practically BSD licence
+# key: pbsd
+# contributor: Ade Attwood <code@adeattwood.co.uk>
+# uuid: pbsd
+# --
+/// <copyright file="`(file-name-nondirectory (buffer-file-name))`" company="Practically.io">
+/// Copyright `(format-time-string "%Y")` Practically.io All rights reserved
+///
+/// Use of this source is governed by a BSD-style
+/// licence that can be found in the LICENCE file or at
+/// https://www.practically.io/copyright/
+/// </copyright>

site-modules/core/files/emacs/snippets/csharp-mode/prop

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: Class property
+# contributor: Ade Attwood <code@adeattwood.co.uk>
+# key: prop
+# uuid: prop
+# --
+public ${1:int} ${2:Name} { get; set; }${3: = ${4:"Default"}}$0

site-modules/core/files/emacs/src/lang/c-sharp.el

@@ -0,0 +1,11 @@
+;;; c-sharp.el --- AMACS -*- lexical-binding: t; -*-
+;;
+;; Copyright 2021 Practically.io All rights reserved
+;;
+;; Use of this source is governed by a BSD-style
+;; licence that can be found in the LICENCE file or at
+;; https://www.practically.io/copyright/
+
+(use-package csharp-mode
+  :ensure t
+  :hook (csharp-mode . lsp-deferred))