Add glslls (#1179)

* Add glslls-based LSP linter
* Make logfile configureable

doc/ale-glsl.txt

@@ -32,5 +32,25 @@ g:ale_glsl_glslang_options                         *g:ale_glsl_glslang_options*
   This variable can be set to pass additional options to glslangValidator.
 
 
+===============================================================================
+glslls                                                        *ale-glsl-glslls*
+
+g:ale_glsl_glslls_executable                     *g:ale_glsl_glslls_executable*
+                                                 *b:ale_glsl_glslls_executable*
+  Type: |String|
+  Default: `'glslls'`
+
+  This variable can be changed to change the path to glslls.
+  See |ale-integrations-local-executables|
+
+g:ale_glsl_glslls_logfile                           *g:ale_glsl_glslls_logfile*
+                                                    *b:ale_glsl_glslls_logfile*
+  Type: |String|
+  Default: `''`
+
+  Setting this variable to a writeable file path will enable logging to that
+  file.
+
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -70,6 +70,7 @@ CONTENTS                                                         *ale-contents*
       fusion-lint.........................|ale-fuse-fusionlint|
     glsl..................................|ale-glsl-options|
       glslang.............................|ale-glsl-glslang|
+      glslls..............................|ale-glsl-glslls|
     go....................................|ale-go-options|
       gofmt...............................|ale-go-gofmt|
       gometalinter........................|ale-go-gometalinter|
@@ -295,7 +296,7 @@ Notes:
 * Erlang: `erlc`, `SyntaxErl`
 * Fortran: `gcc`
 * FusionScript: `fusion-lint`
-* GLSL: glslang
+* GLSL: glslang, `glslls`
 * Go: `gofmt`, `goimports`, `go vet`, `golint`, `gometalinter`!!, `go build`!!, `gosimple`!!, `staticcheck`!!
 * GraphQL: `eslint`, `gqlint`
 * Haml: `haml-lint`