Add rpm spec file linter (rpmlint) (#486)

* Initial attempt at an rpmlint linter.

* Add some basic documentation.

* Play with indentation in the test file.

* Another attempt to fix the rpmlint test.

* Hopefully this does it.

doc/ale-spec.txt

@@ -0,0 +1,28 @@
+===============================================================================
+ALE RPM Spec Integration                                     *ale-spec-options*
+
+
+-------------------------------------------------------------------------------
+rpmlint                                                      *ale-spec-rpmlint*
+
+g:ale_spec_rpmlint_executable                 *g:ale_spec_rpmlint_executable*
+
+  Type: |String|
+  Default: `'rpmlint'`
+
+  This variable sets executable used for rpmlint.
+
+
+g:ale_spec_rpmlint_options                       *g:ale_spec_rpmlint_options*
+
+  Type: |String|
+  Default: `''`
+
+  Set this to pass extra arguments to rpmlint.
+
+  For example, to instruct rpmlint to use a specific configuration file:
+
+  let g:ale_spec_rpmlint_options = '-f custom.cf'
+
+-------------------------------------------------------------------------------
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -71,6 +71,8 @@ CONTENTS                                                         *ale-contents*
     sh....................................|ale-sh-options|
       shell...............................|ale-sh-shell|
       shellcheck..........................|ale-sh-shellcheck|
+    spec..................................|ale-spec-options|
+      rpmlint.............................|ale-spec-rpmlint|
     tex...................................|ale-tex-options|
       chktex..............................|ale-tex-chktex|
       lacheck.............................|ale-tex-lacheck|
@@ -151,6 +153,7 @@ The following languages and tools are supported.
 * Puppet: 'puppet', 'puppet-lint'
 * Python: 'flake8', 'mypy', 'pylint'
 * reStructuredText: 'proselint'
+* RPM spec: 'spec'
 * Rust: 'rustc' (see |ale-integration-rust|)
 * Ruby: 'rubocop'
 * SASS: 'sasslint', 'stylelint'