Add support for bingo (#2165)

* Add support for https://github.com/saibing/bingo
* Add docs for ale-go-bingo
* Use go.mod when found
* Add test for bingo FindProjectRoot
* Simplify ale_linters#go#bingo#GetCommand

test/command_callback/test_bingo_command_callback.vader

@@ -0,0 +1,31 @@
+Before:
+  call ale#assert#SetUpLinterTest('go', 'bingo')
+
+After:
+  Restore
+
+  unlet! b:ale_completion_enabled
+
+  call ale#assert#TearDownLinterTest()
+
+Execute(should set correct defaults):
+  AssertLinter 'bingo', ale#Escape('bingo') . ' --mode stdio'
+
+Execute(should configure bingo callback executable):
+  let b:ale_go_bingo_executable = 'boo'
+  let b:ale_go_bingo_options = ''
+
+  AssertLinter 'boo', ale#Escape('boo')
+
+Execute(should set bingo options):
+  call ale#test#SetFilename('go_paths/go1/prj1/file.go')
+  " let b:ale_completion_enabled = 1
+  let b:ale_go_bingo_options = ''
+
+  AssertLinter 'bingo',
+  \ ale#Escape('bingo') . ''
+
+  let b:ale_go_bingo_options = '--mode stdio --trace'
+
+  AssertLinter 'bingo',
+  \ ale#Escape('bingo') . ' --mode stdio --trace'