Fix launcher not propagating debuggee exit code.
Fix attach-by-PID without explicit --log-dir overriding PTVSD_LOG_DIR (and disabling logging).
Improve test logging, with a separate directory for every test.
Various test fixes.
Fix#1721 "runInTerminal" is broken on non-Windows platforms.
Fix#1722: Output is not captured in "noDebug" with "runInTerminal"
Groundwork for #1713: adapter: multiple concurrent sessions
Move "launch" request parsing and debuggee process spawning, PID reporting and tracking, stdio "output" capture, and exit code reporting into launcher. Launcher now communicates to the adapter via a full-fledged message channel.
Refactor adapter. Add an abstraction for a debug session, and treat IDE, launcher, and debug server as separate components managed by that session.
Improve adapter logging to capture information about current debug session, and current message handler if any.
Fix reporting exceptions from message handlers.
Various test fixes.
Move docstrings to top-level package, and update them to reflect the current behavior.
Remove unused code in ptvsd.common.log.
Move sys.path/prefix/site_packages logging into ptvsd.common.log, and log it from adapter and server to the same level of detail as the tests.
Fix injected code snipped for attach-by-PID.
Fix some Unicode issues in adapter and tests.
Refactor Timeline, debug.Session, and start methods.
Reformat various timeline log entries to improve readability.
Add pretty-printing of composite expectations, to match pretty-printed JSON.
Avoid redundant repetitions of messages when explaining how occurrences matched expectations.
Fix Flask and Django multiprocess tests.
Fix test logs not being captured by pytest.
Fix "import debug_me" check improperly applied in tests where it is unnecessary.
Fix some clarifying patterns not respecting the underlying pattern.
Add pattern helpers for strings: starting_with, ending_with, containing.
Move DAP test helpers to a separate module, and add a helper for frames.
Add support for line markers when setting breakpoints and matching frames.
Assorted test fixes around handling of Unicode and paths.
