Add support for V: "v" (compiler) and "vfmt" fixer. (#3622)

* v: add "v fmt" fixer.

* v: add "v" (build) linter.

* v: fix vlint complaints and add documentation.

* v: add tests.

* v: use ale#Pad().

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

@@ -534,6 +534,9 @@ Notes:
   * `tslint`
   * `tsserver`
   * `typecheck`
+* V
+  * `v`
+  * `vfmt`
 * VALA
   * `uncrustify`
   * `vala_lint`!!