Annotated imports

Presented simple extensions to scala language related to import statements: exported imports, which provide ability to reuse sequence of import clauses in composable form and default rewriters, which provide mechanism for pluggable macro-based AST transformation of overall compilation unit, activated by import of library object. Using these facilities not only allows more compact code, it prevents application programmer from producing certain type of errors too and allows to implement local language extension as libraries on top of standard compiler. Part of discussed extensions is submitted to scala language committee as pre-sip [Ruslan Shevchenko.(2012)] and can be used as first step for refining imports semantics in the future version of scala language.