refactor: Add dev container

- Add `devcontainer.json` and `Dockerfile` with all dependencies necessary to build and test the module, and work on docs with local web server provided by mkdocs.
- Install platyPS during build if module not available in a local or CI build.

.devcontainer/Dockerfile

@@ -0,0 +1,10 @@
+FROM mcr.microsoft.com/powershell:lts-debian-11
+
+SHELL [ "pwsh", "-NoLogo", "-NoProfile", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue'; " ]
+RUN apt update && apt install -y --no-install-recommends libc6-dev python3-pip mkdocs; \
+    pip install mkdocs-material mkdocs-awesome-pages-plugin -q --no-input; \
+    Install-Module Pester -RequiredVersion 5.5.0 -Force; \
+    Install-Module psake -RequiredVersion 4.9.0 -Force; \
+    Install-Module PSReadLine -RequiredVersion 2.3.4 -Force; \
+    Install-Module PSScriptAnalyzer -RequiredVersion 1.21.0 -Force; \
+    Install-Module platyPS -RequiredVersion 0.14.2 -Force;

.devcontainer/devcontainer.json

@@ -0,0 +1,27 @@
+{
+    "name": "PowerShell",
+    "dockerFile": "Dockerfile",
+    "features": {
+        "ghcr.io/devcontainers/features/common-utils:2": {
+            "installZsh": "true",
+            "username": "vscode",
+            "upgradePackages": "false",
+            "nonFreePackages": "true"
+        }
+    },
+    "postCreateCommand": "sudo chsh vscode -s \"$(which pwsh)\"",
+    "customizations": {
+        "vscode": {
+            "settings": {
+                "powershell.powerShellDefaultVersion": "PowerShell",
+                "terminal.integrated.defaultProfile.linux": "pwsh"
+            },
+            "extensions": [
+                "ms-vscode.powershell",
+                "redhat.vscode-yaml",
+                "eamodio.gitlens"
+            ]
+        }
+    },
+    "forwardPorts": [8000]
+}

build.ps1

@@ -8,6 +8,12 @@ param()
 
 $ErrorActionPreference = 'Stop'
 $ProgressPreference = 'SilentlyContinue'
+
+if ($null -eq (Get-Module -ListAvailable -Name platyPS | Where-Object Version -eq '0.14.2')) {
+    Write-Host "Installing platyPS" -ForegroundColor Green
+    Install-Module -Name platyPS -RequiredVersion '0.14.2' -Force -Scope CurrentUser -ErrorAction Stop
+}
+
 $manifest = Import-PowerShellDataFile -Path $PSScriptRoot/ImportExcel/ImportExcel.psd1 
 $outputFolder = Join-Path -Path $PSScriptRoot -ChildPath "Output/ImportExcel/$($manifest.ModuleVersion)"
 
@@ -26,11 +32,13 @@ $Build = @{
 }
 
 # Stage module in output directory
+Write-Host "Copying ./ImportExcel/* to $($Build.Output.Directory)" -ForegroundColor Green
 $null = New-Item -Path $Build.Output.Directory -ItemType Directory -Force
 Get-ChildItem -Path $Build.Output.Directory | Remove-Item -Recurse
 Get-ChildItem -Path ./ImportExcel/ | Copy-Item -Destination $Build.Output.Directory -Recurse
 
 # Embed dot-sourced functions in the PSM1 file
+Write-Host "Merging .PS1 files into ImportExcel.psm1" -ForegroundColor Green
 try {
     Push-Location -Path $Build.Output.Directory
     $usings = @{}
@@ -59,14 +67,14 @@ try {
 
         if ($usings.Count) {
             $usings.Keys | Sort-Object | ForEach-Object {
-                $null = $newPSM1.AppendLine($_)
+                $null = $newPSM1.Append("$_`r`n")
             }
             $usings.Clear()
         }
 
         if ($_ -eq '#region Dot-Sourced Functions') {
             $insideDotSourcedRegion = $true
-            $null = $newPSM1.AppendLine($content)
+            $null = $newPSM1.Append("$content`r`n")
             return
         }
 
@@ -78,7 +86,7 @@ try {
             return
         }
 
-        $null = $newPSM1.AppendLine($_)
+        $null = $newPSM1.Append("$_`r`n")
     }
     if ($content.Length) {
         throw "An error occurred while embedding files from directories referenced in dot-sources.txt.
@@ -92,28 +100,29 @@ try {
 }
 
 # Update docs
+Write-Host "Generating / updating markdown help" -ForegroundColor Green
 Import-Module $Build.Output.ManifestPath -Force
 $null = New-Item -Path $Build.Docs.Directory -ItemType Directory -Force
 $existingHelp = (Get-ChildItem -Path "$($Build.Docs.Directory)/*.md").BaseName
 $newCommands = Get-Command -Module ImportExcel -CommandType Function, Cmdlet | Where-Object Name -NotIn $existingHelp
 if ($existingHelp) {
     $null = Update-MarkdownHelp -Path $Build.Docs.Directory -AlphabeticParamsOrder -ExcludeDontShow
 }
-if ($true) {
+if ($newCommands) {
     $newHelpArgs = @{
         Module                = 'ImportExcel'
         OutputFolder          = $Build.Docs.Directory
         Locale                = $Build.Docs.Locale
         AlphabeticParamsOrder = $true
         ExcludeDontShow       = $true
-        WithModulePage        = $true
         ErrorAction           = 'SilentlyContinue'
     }
     $null = New-MarkdownHelp @newHelpArgs
 }
 
 # Add online help URL for all commands
-$onlineversionpattern = [regex]::new('^online version:.*$', ([RegexOptions]::IgnoreCase, [RegexOptions]::Multiline))
+Write-Host "Updating online help URLs" -ForegroundColor Green
+$onlineversionpattern = [regex]::new('(?<=\n)online version:.*?(?=[\r\n])', ([RegexOptions]::IgnoreCase, [RegexOptions]::Multiline))
 foreach ($path in [io.directory]::EnumerateFiles($Build.Docs.Directory, '*.md')) {
     $baseName = ([fileinfo]$path).BaseName
     $content = [file]::ReadAllText($path)