Add psalm linter for PHP (#1893)

test/command_callback/test_psalm_command_callbacks.vader

@@ -0,0 +1,12 @@
+Before:
+  call ale#assert#SetUpLinterTest('php', 'psalm')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(Custom executables should be used for the executable and command):
+  let g:ale_php_psalm_executable = 'psalm_test'
+
+  AssertLinter 'psalm_test',
+  \ ale#Escape('psalm_test') . ' --diff --output-format=emacs %s'
+

test/handler/test_php_psalm_handler.vader

@@ -0,0 +1,24 @@
+Before:
+  runtime ale_linters/php/psalm.vim
+
+After:
+  call ale#linter#Reset()
+
+Execute(The php static analyzer handler should parse errors from psalm):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'type': 'W',
+  \     'text': 'somewarning',
+  \   },
+  \   {
+  \     'lnum': 11,
+  \     'type': 'E',
+  \     'text': 'someerror',
+  \   },
+  \ ],
+  \ ale_linters#php#psalm#Handle(347, [
+  \ "/file:1:3:warning - somewarning",
+  \ "/file:11:33:error - someerror",
+  \ ])