Added build script
Updated build instruction in README to mention ``./build.sh`` script.
Added CONTRIBUTING doc
Pass `file.encoding`` VM argument to process that executes the worksheet

* Don't use interpolated string in test ``WorksheetEvalTest.unicodeCharactersAreAllowed``
   for keeping compatibility with Scala 2.9.
* Disabled test ``WorksheetEvalTest.unicodeCharactersAreAllowed`` because it fails from
   the command line when executed on MacOSX (I'll re-open ticket #124).
* Pass the ``file.encoding`` to the JVM used to execute the instrumented worksheet source.
   This is necessary for the result output to be in the right encoding.
* Added an ``encoding`` member to the ``DocumentHolder`` to reduce duplication.
Set file encoding to `UTF-8` for tests execution in Tycho

* Had to change the return type of the Snowman to `AnyRef` for
  the test to pass against both Scala 2.9 and Scala 2.10 (the
  returned name for the `String` type is different in 2.9 and
  2.10)

* Pass `-Dfile.encoding=UTF-8` to Tycho test task.
* Re-enabled encoding test.

Fix #120
Allow users to specify VM arguments

Added preference for specifying VM arguments to be used by worksheet processes.
Adjusted preference page layout to accomodate for new field
Error dialog reports last output upon abnormal worksheet termination

Fix #125