Added CHANGELOG document

Author: vladar

CHANGELOG.md

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+# Changelog
+
+## v0.10.0
+This release brings several breaking changes. Please refer to [UPGRADE](UPGRADE.md) document for details.
+
+New features and notable changes:
+- Changed minimum PHP version from 5.4 to 5.5
+- Lazy loading of types without separate build step (see #69, see [docs](docs/type-system/schema.md#lazy-loading-of-types))
+- PSR-7 compliant Standard Server (see [docs](docs/executing-queries.md#using-server))
+- New default error formatting, which does not expose sensitive data (see [docs](docs/error-handling.md))
+- Ability to define custom error handler to filter/log/re-throw exceptions after execution (see [docs](docs/error-handling.md#custom-error-handling-and-formatting))
+- Allow defining schema configuration using objects with fluent setters vs array (see [docs](docs/type-system/schema.md#using-config-class))
+- Allow serializing AST to array and re-creating AST from array lazily (see [docs](docs/reference.md#graphqlutilsast))
+- [Apollo-style](https://dev-blog.apollodata.com/query-batching-in-apollo-63acfd859862) query batching support via server (see [docs](docs/executing-queries.md#query-batching))
+
+Improvements:
+- Significantly improved parser performance (see #137 and #128)
+- Support for PHP7 exceptions everywhere (see #127)
+- Ability to pass custom config formatter when defining schema using [GraphQL type language](http://graphql.org/learn/schema/#type-language) (see [docs](docs/type-system/type-language.md))
+- Improved [documentation](http://webonyx.github.io/graphql-php/) and docblock comments
+
+Deprecations and breaking changes - see [UPGRADE](UPGRADE.md) document.
+
+#### v0.9.14
+- Minor change to assist DataLoader project in fixing #150 
+
+#### v0.9.13
+- Fixed PHP notice and invalid conversion when non-scalar value is passed as ID or String type (see #121) 
+
+#### v0.9.12
+- Fixed bug occurring when enum `value` is bool, null or float (see #141)
+
+#### v0.9.11
+- Ability to disable introspection (see #131)
+
+#### v0.9.10
+- Fixed issue with query complexity throwing on invalid queries (see #125)
+- Fixed "Out of memory" error when `resolveType` returns unexpected result (see #119)
+
+#### v0.9.9
+- Bugfix: throw UserError vs InvariantViolationError for errors caused by client (see #123)
+
+#### v0.9.8
+- Bugfix: use directives when calculating query complexity (see #113)
+- Bugfix: `AST\Node::__toString()` will convert node to array recursively to encode to json without errors
+
+#### v0.9.7
+- Bugfix: `ResolveInfo::getFieldSelection()` now correctly merges fragment selections (see #98)
+
+#### v0.9.6
+- Bugfix: `ResolveInfo::getFieldSelection()` now respects inline fragments
+
+#### v0.9.5
+- Fixed SyncPromiseAdapter::all() to not change the order of arrays (see #92)
+
+#### v0.9.4
+- Tools to help building schema out of Schema definition language as well as printing existing 
+schema in Schema definition language (see #91)
+
+#### v0.9.3
+- Fixed Utils::assign() bug related to detecting missing required keys (see #89)
+
+#### v0.9.2
+- Schema Definition Language: element descriptions can be set through comments (see #88)
+
+#### v0.9.1
+- Fixed: `GraphQL\Server` now properly sets promise adapter before executing query
+
+## v0.9.0
+- Deferred resolvers (see #66, see [docs](docs/data-fetching.md#solving-n1-problem))
+- New Facade class with fluid interface: `GraphQL\Server` (see #82)
+- Experimental: ability to load types in Schema lazily via custom `TypeResolutionStrategy` (see #69)
+
+
+## v0.8.0
+This release brings several minor breaking changes. Please refer to [UPGRADE](UPGRADE.md) document for details.
+
+New features:
+- Support for `null` value (as required by latest GraphQL spec)
+- Shorthand definitions for field and argument types (see #47)
+- `path` entry in errors produced by resolvers for better debugging
+- `resolveType` for interface/union is now allowed to return string name of type
+- Ability to omit name when extending type class (vs defining inline)
+
+Improvements:
+- Spec compliance improvements
+- New docs and examples
+
+## Older versions
+Look at [Github Releases Page](https://github.com/webonyx/graphql-php/releases).