Add PSGallery publishing support

BuildTasks/PublishModule.Task.ps1

@@ -0,0 +1,25 @@
+task PublishModule {
+
+    if ( $ENV:BHBuildSystem -ne 'Unknown' -and
+        $ENV:BHBranchName -eq "master" -and
+        [string]::IsNullOrWhiteSpace($ENV:APPVEYOR_PULL_REQUEST_NUMBER) -and
+        -not [string]::IsNullOrWhiteSpace($ENV:NugetApiKey))
+    {
+        $publishModuleSplat = @{
+            Path        = $Destination
+            NuGetApiKey = $ENV:NugetApiKey
+            Verbose     = $true
+            Force       = $true
+            Repository  = $PSRepository
+            ErrorAction = 'Stop'
+        }
+        Publish-Module @publishModuleSplat
+    }
+    else
+    {
+        "Skipping deployment: To deploy, ensure that...`n" +
+        "`t* You are in a known build system (Current: $ENV:BHBuildSystem)`n" +
+        "`t* You are committing to the master branch (Current: $ENV:BHBranchName) `n" +
+        "`t* This is not a pull request"
+    }
+}