popen wip
Added CommandExecutor class.
Added generic exec command using popen. Added error_file log.
Added missing error_file parameter.
Added missing option in command line description.
Added missing description for err-file parameter;
Added missing parameter err-file.
Use class CommandExecutor.
Use popen to start any process.
Now uses ProcessError exception management everywhere.
Fixed help.
Now uses output file instead of error file.
Updated exception logging on top level.
Merge pull request #13 from deviantony/popen

Use popen to execute processes.