Implementation of Java Debug Interface in Haskell.

Current implementation only works with Java stratum as default.

Right now some of functions are located in Impl module some functions are
located in corresponding modules like ReferenceType and Field.

This is an intermediate state and majority of functions are in Impl module
whereas they are supposed to be each in its corresponding module. However there
is a number of functions that can't be put in the modules because they are used
by several modules and GHC doesn't allow dependency loops. That is why some
functions will stay in Impl module.

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