feat: Add protolint as linter and fixer (#2911)

doc/ale-proto.txt

@@ -5,14 +5,15 @@ ALE Proto Integration                                         *ale-proto-options
 ===============================================================================
 Integration Information
 
-Linting of `.proto` files requires that the `protoc` binary is installed in the
-system path and that the `protoc-gen-lint` plugin for the `protoc` binary is also
-installed.
-
 To enable `.proto` file linting, update |g:ale_linters| as appropriate:
 >
   " Enable linter for .proto files
-  let g:ale_linters = {'proto': ['protoc-gen-lint']}
+  let g:ale_linters = {'proto': ['protoc-gen-lint', 'protolint']}
+
+To enable `.proto` file fixing, update |g:ale_fixers| as appropriate:
+>
+  " Enable linter for .proto files
+  let b:ale_fixers = {'proto': ['protolint']}
 <
 ===============================================================================
 protoc-gen-lint                                      *ale-proto-protoc-gen-lint*
@@ -29,5 +30,31 @@ g:ale_proto_protoc_gen_lint_options       *g:ale_proto_protoc_gen_lint_options*
   directory of the linted file is always passed as an include path with '-I'
   before any user-supplied options.
 
+===============================================================================
+protolint                                                   *ale-proto-protolint*
+
+  The linter is a pluggable tool that doesn't depend on the `protoc` binary.
+  This supports both linting and fixing.
+  Make sure the binary is available in the system path, or set
+  ale_proto_protolint_executable.
+  Note that the binary with v0.22.0 or above is supported.
+
+g:ale_proto_protolint_executable             *g:ale_proto_protolint_executable*
+
+  Type: |String|
+  Default: 'protolint'
+
+  This variable can be changed to modify the executable used for protolint.
+
+g:ale_proto_protolint_config                     *g:ale_proto_protolint_config*
+
+  Type: |String|
+  Default: `''`
+
+  A path to a protolint configuration file.
+
+  The path to the configuration file can be an absolute path or a relative
+  path. ALE will search for the relative path in parent directories.
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

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

@@ -385,6 +385,7 @@ Notes:
   * `swipl`
 * proto
   * `protoc-gen-lint`
+  * `protolint`
 * Pug
   * `pug-lint`
 * Puppet

doc/ale.txt

@@ -2918,6 +2918,7 @@ documented in additional help files.
     swipl.................................|ale-prolog-swipl|
   proto...................................|ale-proto-options|
     protoc-gen-lint.......................|ale-proto-protoc-gen-lint|
+    protolint.............................|ale-proto-protolint|
   pug.....................................|ale-pug-options|
     puglint...............................|ale-pug-puglint|
   puppet..................................|ale-puppet-options|