Add metadebugger_command_handler
Factor out metadebugger_command from a simple std::tuple
Add tests for metadebugger_command
metadebugger_command_handler now doesn't touch mdb_shell directly
Add test_ prefix for mdb_command tests
Fix typo in file name
Make get_command_for_line const
Fix algorithm in metadebugger command parsing

The appeared when a command was a prefix of another command
Use C++11 style vector initialization
Add tests for metadebugger command parsing