4.0.0: Drop PHP 5 support

• Implemented xp-framework/rfc#334: Drop PHP 5.6:
  . Heads up: Minimum required PHP version now is PHP 7.0.0
  . Rewrote code base, grouping use statements
  . Converted newinstance to anonymous classes
  (@thekid)

3.1.1: XP10 compatibility

• Added compatibility with XP 10.0.0 - @thekid

3.1.0: Member acces

• Made Box::$value, ListOf::$backing and ListIndexedBy::$indexed
  members accessible from subclasses by declaring them protected
  (@thekid)
• Ensured PHP 7.2 compatibility - @thekid

3.0.1: ListOf fix

• Fixed lang.partial.ListOf to also declare hashCode() so that
  classes using this trait will be able to implement lang.Value
  (@thekid)

3.0.0: XP9 Compatibiliy

• Added forward compatibility with XP 9.0.0 - @thekid

2.1.1: Weird fatals fix

• Fixed issue #14: Weird fatals - @thekid

2.1.0: XP8 Compatibility

• Added forward compatibility with XP 8.0.0 - @thekid

2.0.0: Drop PHP 5.5 support

• Heads up: Dropped PHP 5.5 support! Minimum PHP version required
  is now PHP 5.6. See PR #17
  (@thekid)

1.1.2: Mirrors 4.X support

• Made compatible with xp-forge/mirrors 4.0-SERIES - @thekid

1.1.1: Builder fixes

• Fixed errors when using instance creation with keywords in PHP 5.x
  (@thekid)