make options for credo configurable (#2337)

* Add credo --strict option

If a user sets 'let g:ale_elixir_credo_strict=1' it will run credo with
--strict instead of suggest.  The default (0) is to run as suggest.

* Added credo docs

1 files changed, 28 insertions, 0 deletions

diff --git a/test/command_callback/test_elixir_credo.vader b/test/command_callback/test_elixir_credo.vader
new file mode 100644
index 00000000..1a146db8
--- /dev/null
+++ b/test/command_callback/test_elixir_credo.vader
@@ -0,0 +1,28 @@
+Before:
+  call ale#assert#SetUpLinterTest('elixir', 'credo')
+  call ale#test#SetFilename('elixir_paths/mix_project/lib/app.ex')
+
+
+After:
+  unlet! g:ale_elixir_credo_strict
+
+  call ale#assert#TearDownLinterTest()
+
+Execute(Builds credo command with --strict mode when set to 1):
+  let g:ale_elixir_credo_strict = 1
+
+  AssertLinter 'mix',
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/elixir_paths/mix_project'))
+  \ . 'mix help credo && mix credo --strict --format=flycheck --read-from-stdin %s'
+
+Execute(Builds credo command with suggest mode by default):
+  AssertLinter 'mix',
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/elixir_paths/mix_project'))
+  \ . 'mix help credo && mix credo suggest --format=flycheck --read-from-stdin %s'
+
+Execute(Builds credo command with suggest mode when set to 0):
+  let g:ale_elixir_credo_strict = 0
+
+  AssertLinter 'mix',
+  \ ale#path#CdString(ale#path#Simplify(g:dir . '/elixir_paths/mix_project'))
+  \ . 'mix help credo && mix credo suggest --format=flycheck --read-from-stdin %s'