Clean out intermediate and output files of compilation process.

There should be no files in the repository that are auto-generated as
part of the compilation and test process.

Therefore files in Source/BIN/Release/ConverterPlugins have been deleted.
BuildLog.htm have been deleted.
Output files of flex/bison (parser.h + lexer.c files) have been deleted.

The gitignore file has been modified to keep such things out of the repository.

Signed-off-by: Tobias Lorenz <tobias.lorenz@etas.com>