Linter for powershell syntax errors (#2413)

* Linter for powershell syntax errors

doc/ale-powershell.txt

@@ -2,6 +2,21 @@
 ALE PowerShell Integration                             *ale-powershell-options*
 
 
+===============================================================================
+powershell                                          *ale-powershell-powershell*
+
+g:ale_powershell_powershell_executable  *g:ale_powershell_powershell_executable*
+                                        *b:ale_powershell_powershell_executable*
+  Type: String
+  Default: `'pwsh'`
+
+  This variable can be changed to use a different executable for powershell.
+
+>
+  " Use powershell.exe rather than the default pwsh
+  let g:ale_powershell_powershell_executable = 'powershell.exe'
+>
+
 ===============================================================================
 psscriptanalyzer                              *ale-powershell-psscriptanalyzer*
 

doc/ale-supported-languages-and-tools.txt

@@ -319,6 +319,7 @@ Notes:
 * Pony
   * `ponyc`
 * PowerShell
+  * `powershell`
   * `psscriptanalyzer`
 * Prolog
   * `swipl`

doc/ale.txt

@@ -2070,6 +2070,7 @@ documented in additional help files.
   pony....................................|ale-pony-options|
     ponyc.................................|ale-pony-ponyc|
   powershell............................|ale-powershell-options|
+    powershell..........................|ale-powershell-powershell|
     psscriptanalyzer....................|ale-powershell-psscriptanalyzer|
   prolog..................................|ale-prolog-options|
     swipl.................................|ale-prolog-swipl|