Add VHDL Support & Newer Verilog Linters (#2229)

* Added VHDL file support with ghdl compiler
* Update ghdl.vim
* Create vcom.vim
* Create xvhdl.vim
* Update xvlog.vim
* Added documentation for VHDL & Verilog linters
* Added tests to VHDL & Verilog linters

doc/ale.txt

@@ -348,6 +348,12 @@ CONTENTS                                                         *ale-contents*
     verilog/systemverilog.................|ale-verilog-options|
       iverilog............................|ale-verilog-iverilog|
       verilator...........................|ale-verilog-verilator|
+      vlog................................|ale-verilog-vlog|
+      xvlog...............................|ale-verilog-xvlog|
+    vhdl..................................|ale-vhdl-options|
+      ghdl................................|ale-vhdl-ghdl|
+      vcom................................|ale-vhdl-vcom|
+      xvhdl...............................|ale-vhdl-xvhdl|
     vim...................................|ale-vim-options|
       vint................................|ale-vim-vint|
     vim help..............................|ale-vim-help-options|
@@ -511,7 +517,8 @@ Notes:
 * Thrift: `thrift`
 * TypeScript: `eslint`, `prettier`, `tslint`, `tsserver`, `typecheck`
 * VALA: `uncrustify`
-* Verilog: `iverilog`, `verilator`
+* Verilog: `iverilog`, `verilator`, `vlog`, `xvlog`
+* VHDL: `ghdl`, `vcom`, `xvhdl`
 * Vim: `vint`
 * Vim help^: `alex`!!, `proselint`, `write-good`
 * Vue: `prettier`, `vls`