2.0.0: New lambda syntax, namespaces and 5.3 closures

This release contains the following changes:

• Made available via Composer (@thekid)
• Heads up: Changed minimum XP version to run the XP compiler to XP
  6.0.0. It can still generated code to run on XP 5.X-SERIES, but will
  require 6.X-SERIES to run itself (@thekid)
• Added possibility to add default values to lambda parameters. See
  #38 - (@thekid)
• Fixed compiler choking on methods with generic return types (@thekid)
• Allowed omitting the parameter type inside method declarations. The type
  will then be set to var and will be unchecked at runtime (@thekid)
• Changed syntax for lambdas from #{ $a -> $a + 1 }; to $a -> $a + 1;,
  after resolving the grammar conflicts the former was avoiding. The old
  form is still supported but will raise compile-time warnings. It will be
  removed in the next major release.
  (@thekid)
• Changed PHP 5.3 emitter to emit PHP 5.3 anonymous functions for lambdas
  (@thekid)
• Merged pull request #37 to solve issue #36: Support "new T()", "T::const"
  and "T::$static" inside annotations - (@thekid)
• Added backwards compatible emitter (-E php5.2) to create non-namespaced
  code for use with XP 5.8 and PHP 5.2 - (@thekid)
• Changed default behaviour to creating namespaced code (compatible with
  XP 5.9 and PHP 5.3+) - (@thekid)
• Changed "-E" command line argument to support versions: -E name will
  load xp.compiler.emit.name.Emitter, -E name60 will load the class
  xp.compiler.emit.name.V60Emitter - (@thekid)
• Changed all emit*() methods in xp.compiler.emit.Emitter to protected
  (@thekid)