Move workspace from "engine" directory to repository root

The initial rationale behind pushing all files into a subdirectory was keeping
the repository root clean, however there's probably better, and move meaningful
ways of doing so (splitting `engine`, `context`, and `value` to separate
packages, moving all `.c` files into the `src` directory etc.

context_test.go

@@ -218,7 +218,7 @@ var bindTests = []struct {
 	},
 	{
 		3.14159,
-		"d:3.1415899999999999;",
+		"d:3.14159;",
 	},
 	{
 		true,

php.go

@@ -1,18 +0,0 @@
-// Copyright 2016 Alexander Palaistras. All rights reserved.
-// Use of this source code is governed by the MIT license that can be found in
-// the LICENSE file.
-
-// Package php implements bindings from Go to PHP, and allows for executing
-// scripts, binding variables and defining functions and classes which can then
-// be called from within PHP scripts.
-package php
-
-import (
-	"github.com/deuill/go-php/engine"
-)
-
-// New initializes a PHP engine instance on which contexts can be executed. It
-// corresponds to PHP's MINIT (module init) phase.
-func New() (*engine.Engine, error) {
-	return engine.New()
-}