Reimplement PowerShell lexer (#1213)

The existing PowerShell lexer subclasses the Shell lexer and
extends/modifies its rules. However, while PowerShell is a shell, its
syntax and grammar is far richer than other shells. This commit replaces
the existing lexer with a new lexer that is independent of the Shell lexer.

lib/rouge/demos/powershell

@@ -1,49 +1,13 @@
-Function Get-IPv4Scopes
-<#
-	.SYNOPSIS
-		Read IPv4Scopes from an array of servers
-	.PARAMETER Servers
-		Specifies an array of servers
-	.EXAMPLE
-		Get-IPv4Scopes
-
-		Will prompt for all inputs
-#>
+function Verb-Noun
 {
-    [CmdletBinding()]
-    Param(
-    # 1
-    [parameter(
-        Mandatory=$true,
-        Position=0,
-        ValueFromPipelineByPropertyName=$true,
-        HelpMessage="Server List"
-        )]
-    [string[]]$Servers,
-    #2
-    [parameter(Mandatory=$false,ValueFromPipeline=$false)]
-    [bool]$Unique=$false
-    )  #EndParam
-
-    Begin {}
-
-    Process {
-        $arrayJobs=@()
-        foreach ($server in $Servers) {
-            $arrayJobs+=Invoke-Command -ComputerName $server -scriptblock {Get-DhcpServerv4Scope}  -AsJob
-        }
-        $complete=$false
-        while (-not $complete) {
-            $arrayJobsInProgress= $arrayJobs | Where-Object { $_.State -match 'running' }
-            if (-not $arrayJobsInProgress) { $complete=$true }
-        }
-        $Scopes=$arrayJobs|Receive-Job
-        $UniqueScopes=$Scopes|Sort-Object -Property ScopeId -Unique
-    }
-
-    End {
-        if ($Unique) { return $UniqueScopes }
-        else { return $Scopes }
-    }
-
-} #end function
+    <#
+    .SYNOPSIS
+    Tells you what it does
+
+    .DESCRIPTION
+    Tells you what it does with more detail.
+    #>
+    param ([string]$Name, [string]$Extension = "txt", [string]$foo="bar")
+    $name = $name + "." + $extension
+    $name
+}