5.0.0: XP7 compatibility

• Added version compatibility with XP 7 - @thekid

4.1.2: XP7 Forward compatibility

• Fix code to use nameof() instead of the deprecated getClassName()
  method from lang.Generic. See xp-framework/core#120
  (@thekid)

4.1.1: Forward compatible dependencies declaration

• Added dependencies on collections and unittest libraries which have
  since been extracted from XP core.
  (@thekid)

4.1.0: Collectors

• Merged PR #28: Fix Collectors class' methods to cast given functions
  (@thekid)
• Merged PR #27: Add support for optional mapper in toSet() and toList()
  (@thekid)

4.0.0: Enter PHP 5.5

• Heads up: Dropped PHP 5.4 support. See pull request #26. Note: As
  the main source is not touched, unofficial PHP 5.4 support is still
  available though not tested with Travis-CI.
  (@thekid)

3.1.0: Key to success

• Merged PR #25: Implement support for using keys in collect() - @thekid
• Merged PR #24: Implement support for mapping keys - @thekid

3.0.0: Value object protocol

• Renamed whenNull() to whenAbsent() in util.data.Optional. This is
  more consistent with the present() method. See pull request #23
  (@thekid)
• Implemented Optional::toString(), equals() and hashCode() - @thekid
• Implemented Sequence::toString(), equals() and hashCode() - @thekid

2.2.1: HHVM support

• Fixed issue #22: tests not running on HHVM - @thekid

2.2.0: Optional features

• Made Optional's constructor public and allow new Optional(null) to
  represent an optional with a present null value
  (@thekid)
• Changed Optional::of() to return an empty optional if null is passed
  (@thekid)
• Added whenNull() method to util.data.Optional to allow easy chaining
  (@thekid)
• Added filter(), map() and orUse() implementations to util.data.Optional
  See pull request #21
  (@thekid)

2.1.1: Bugfix with sorted()

• Don't keep index association when sorting, this yields arrays like
  [1 => 'second', 0 => 'first']. These arrays are not zero-based and
  considered maps e.g. by typeof()
  (@thekid)