[#253] DAP initialization sequence

Description

Problem: we have a parser for DAP and can successfully read VSCode's messages, but we don't answer to them, so VSCode does not consider our debugger initialized and ready to run.

Solution: implement DAP writer thread which accepts DAP messages and writes them to stdout. Handle DAP messages that are related to the initialization of the adapter. At this point VSCode thinks that we are initialized and that the debuggee is running.

Related issue(s)

Resolves #253 (closed)

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