Document and test ale_python_vulture_options

The vulture linter already supports ale_python_vulture_options, but it
is not documented or tested.  Since vulture only supports configuration
via options, it is an important use case.  Add docs and test.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

doc/ale-python.txt

@@ -671,6 +671,15 @@ g:ale_python_vulture_executable               *g:ale_python_vulture_executable*
   See |ale-integrations-local-executables|
 
 
+g:ale_python_vulture_options                     *g:ale_python_vulture_options*
+                                                 *b:ale_python_vulture_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to add command-line arguments to the vulture
+  invocation.
+
+
 g:ale_python_vulture_use_global               *g:ale_python_vulture_use_global*
                                               *b:ale_python_vulture_use_global*
   Type: |Number|

test/command_callback/test_vulture_command_callback.vader

@@ -0,0 +1,68 @@
+Before:
+  call ale#assert#SetUpLinterTest('python', 'vulture')
+  call ale#test#SetFilename('test.py')
+
+  let b:bin_dir = has('win32') ? 'Scripts' : 'bin'
+
+After:
+  unlet! b:bin_dir
+  unlet! b:executable
+
+  call ale#assert#TearDownLinterTest()
+
+Execute(The vulture command callback should lint file directory by default):
+  AssertLinter 'vulture',
+  \ ale#path#BufferCdString(bufnr(''))
+  \   . ale#Escape('vulture') . '  .'
+
+Execute(The vulture command callback should lint project root, when present):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/no_virtualenv/subdir/foo/bar.py')
+
+  AssertLinter 'vulture',
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/python_paths/no_virtualenv/subdir'))
+  \   . ale#Escape('vulture') . '  .'
+
+Execute(The option for disabling change directory works and only lints file):
+  let g:ale_python_vulture_change_directory = 0
+
+  AssertLinter 'vulture', ale#Escape('vulture') . '  %s'
+
+Execute(The vulture executable should be configurable, and escaped properly):
+  let g:ale_python_vulture_executable = 'executable with spaces'
+
+  AssertLinter 'executable with spaces',
+  \ ale#path#BufferCdString(bufnr(''))
+  \   . ale#Escape('executable with spaces') . '  .'
+
+Execute(The vulture command callback should let you set options):
+  let g:ale_python_vulture_options = '--some-option'
+
+  AssertLinter 'vulture',
+  \ ale#path#BufferCdString(bufnr(''))
+  \   . ale#Escape('vulture') . ' --some-option .'
+
+Execute(The vulture command callback should detect virtualenv directories and switch to the project root):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py')
+
+  let b:executable = ale#path#Simplify(
+  \ g:dir . '/python_paths/with_virtualenv/env/' . b:bin_dir . '/vulture'
+  \)
+
+  AssertLinter b:executable,
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/subdir'))
+  \   . ale#Escape(b:executable) . '  .'
+
+Execute(You should able able to use the global vulture instead):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py')
+  let g:ale_python_vulture_use_global = 1
+
+  AssertLinter 'vulture',
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/subdir'))
+  \   . ale#Escape('vulture') . '  .'
+
+Execute(Setting executable to 'pipenv' appends 'run vulture'):
+  let g:ale_python_vulture_executable = 'path/to/pipenv'
+
+  AssertLinter 'path/to/pipenv',
+  \ ale#path#BufferCdString(bufnr(''))
+  \   . ale#Escape('path/to/pipenv') . ' run vulture' . '  .'