Add PhpStan (PHP Static Code Analyser) PreCommit Hook

Added [PhpStan](https://github.com/phpstan/phpstan) PreCommit Hook.

**Example Files Change**

```
// app/foo.php
<?php

namespace App;

class Foo
{
    public function __construct($foo, $test)
    {
        $this->foo = $foo;
    }
}

// app/bar.php
<?php

namespace App;

class Bar
{
    public function __construct($foo)
    {
        $this->foo = $foo;
    }

    private function testMe()
    {
        return $this->hello;
    }
}
```

**Example Error Messages***

```
Running pre-commit hooks
Analysing PHP codes...............................[PhpStan] FAILED
Errors on modified lines:
/app/bar.php:9:Access to an undefined property App\Bar::$foo.
/app/bar.php:14:Access to an undefined property App\Bar::$hello.
/app/foo.php:7:Constructor of class App\Foo has an unused parameter $test.
/app/foo.php:9:Access to an undefined property App\Foo::$foo.

✗ One or more pre-commit hooks failed
```

Author: taufek

README.md

@@ -530,6 +530,7 @@ issue](https://github.com/brigade/overcommit/issues/238) for more details.
 * [NginxTest](lib/overcommit/hook/pre_commit/nginx_test.rb)
 * [PhpCs](lib/overcommit/hook/pre_commit/php_cs.rb)
 * [PhpLint](lib/overcommit/hook/pre_commit/php_lint.rb)
+* [PhpStan](lib/overcommit/hook/pre_commit/php_stan.rb)
 * [Pronto](lib/overcommit/hook/pre_commit/pronto.rb)
 * [PuppetLint](lib/overcommit/hook/pre_commit/puppet_lint.rb)
 * [PuppetMetadataJsonLint](lib/overcommit/hook/pre_commit/puppet_metadata_json_lint.rb)

config/default.yml

@@ -498,6 +498,14 @@ PreCommit:
     flags: ['--standard=PSR2', '--report=csv']
     include: '**/*.php'
 
+  PhpStan:
+    description: 'Analyze with phpstan'
+    enabled: false
+    command: 'phpstan'
+    flags: ['analyze', '--errorFormat=raw']
+    include:
+      - '**/*.php'
+
   Pronto:
     enabled: false
     description: 'Analyzing with pronto'

lib/overcommit/hook/pre_commit/php_stan.rb

@@ -0,0 +1,28 @@
+module Overcommit::Hook::PreCommit
+  # Runs `phpstan` against any modified PHP files.
+  # For running `phpstan` with Laravel, it requires setup with `ide_helper`.
+  #
+  # References:
+  # https://github.com/phpstan/phpstan/issues/239
+  # https://gist.github.com/edmondscommerce/89695c9cd2584fefdf540fb1c528d2c2
+  class PhpStan < Base
+    MESSAGE_REGEX = /^(?<file>.+)\:(?<line>\d+)\:(?<message>.+)/
+
+    def run
+      messages = []
+
+      result = execute(command, args: applicable_files)
+
+      unless result.success?
+        messages += result.stdout.lstrip.split("\n")
+      end
+
+      return :pass if messages.empty?
+
+      extract_messages(
+        messages,
+        MESSAGE_REGEX
+      )
+    end
+  end
+end

spec/overcommit/hook/pre_commit/php_stan_spec.rb

@@ -0,0 +1,47 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::PreCommit::PhpStan do
+  let(:config)  { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context) { double('context') }
+  subject { described_class.new(config, context) }
+
+  before do
+    subject.stub(:applicable_files).and_return(%w[sample.php])
+  end
+
+  context 'when phpstan exits successfully' do
+    before do
+      sample_output = ''
+
+      result = double('result')
+      result.stub(:success?).and_return(true)
+      result.stub(:stdout).and_return(sample_output)
+      result.stub(:status).and_return(0)
+      subject.stub(:execute).and_return(result)
+    end
+
+    it { should pass }
+  end
+
+  context 'when phpstan exits unsuccessfully' do
+    let(:result) { double('result') }
+
+    before do
+      result.stub(:success?).and_return(false)
+      result.stub(:status).and_return(2)
+      subject.stub(:execute).and_return(result)
+    end
+
+    context 'and it reports a warning' do
+      before do
+        sample_output = [
+          '/sample1.php:14:Call to an undefined static method Sample1::where()',
+          '/sample2.php:17:Anonymous function has an unused use $myVariable.'
+        ].join("\n")
+        result.stub(:stdout).and_return(sample_output)
+      end
+
+      it { should fail_hook }
+    end
+  end
+end