2.6.0: Unicode escape sequences

• Implemented support unicode escape sequences in PHP 5.6, see #38
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• Fixed issue #39: Syntax error for parameters called "function"
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• Dropped confusing way of compiling multiple sources using -b to
  strip bases. New way is to pass multiple directories directly, e.g.
  $ xp compile -o dist src/main/php/ src/test/php
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• Fixed compiling to a directory when the source path was not inside
  the current directory.
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