Add a linter for Apache Thrift IDL files

This linter works by invoking the `thrift` compiler with the buffer
contents and reporting any parser and code generation issues.

The handler rolls its own output-matching loop because we have the
(unfortunate) requirement of handling error output that spans multiple
lines.

Unit tests cover both the command callback and handler, and there is
initial documentation for all of the option variables.

doc/ale-thrift.txt

@@ -0,0 +1,46 @@
+===============================================================================
+ALE Thrift Integration                                     *ale-thrift-options*
+
+
+===============================================================================
+thrift                                                      *ale-thrift-thrift*
+
+The `thrift` linter works by compiling the buffer's contents and reporting any
+errors reported by the parser and the configured code generator(s).
+
+g:ale_thrift_thrift_executable                 *g:ale_thrift_thrift_executable*
+                                               *b:ale_thrift_thrift_executable*
+  Type: |String|
+  Default: `'thrift'`
+
+  See |ale-integrations-local-executables|
+
+
+g:ale_thrift_thrift_generators                 *g:ale_thrift_thrift_generators*
+                                               *b:ale_thrift_thrift_generators*
+  Type: |List| of |String|s
+  Default: `['cpp']`
+
+  This list must contain one or more named code generators. Generator options
+  can be included as part of each string, e.g. `['py:dynamic']`.
+
+
+g:ale_thrift_thrift_includes                     *g:ale_thrift_thrift_includes*
+                                                 *b:ale_thrift_thrift_includes*
+  Type: |List| of |String|s
+  Default: `[]`
+
+  This list contains paths that will be searched for thrift `include`
+  directives.
+
+
+g:ale_thrift_thrift_options                       *g:ale_thrift_thrift_options*
+                                                  *b:ale_thrift_thrift_options*
+  Type: |String|
+  Default: `'-strict'`
+
+  This variable can be changed to customize the additional command-line
+  arguments that are passed to the thrift compiler.
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -127,6 +127,8 @@ CONTENTS                                                         *ale-contents*
     tex...................................|ale-tex-options|
       chktex..............................|ale-tex-chktex|
       lacheck.............................|ale-tex-lacheck|
+    thrift................................|ale-thrift-options|
+      thrift..............................|ale-thrift-thrift|
     typescript............................|ale-typescript-options|
       eslint..............................|ale-typescript-eslint|
       tslint..............................|ale-typescript-tslint|
@@ -248,6 +250,7 @@ Notes:
 * Tcl: `nagelfar`!!
 * Texinfo: `proselint`
 * Text^: `proselint`, `vale`
+* Thrift: `thrift`
 * TypeScript: `eslint`, `tslint`, `tsserver`, `typecheck`
 * Verilog: `iverilog`, `verilator`
 * Vim: `vint`