Update .gitignore.

Remove file excludes.
Add tmp directory exclude.
Update conversation class.

- Add method get_participant_names to return
    a comma seperated list of participant names
- Update get_events method,
    implement sorting algorithm.
Update get_formatted_message.

Implement message formatting the right way.
Update event_list class.

- Update constructor, remove unnecessary code.
- Implement get_events method to return
    an array of the events in the list ( hash )
Update main class.

- Update output format of conversations overview
- Update time output for single events in conversations
- Fetch possible exception while getting message_content
Update participant list class.

- Clean up constructor, remove unnecessary code.
- Implement method to return a comma seperated list of participants.
Remove unnecessary code.

- Remove get_paticipants_names method
    because we can get that over the participants themself.
- Remove unnecessary comment for testing how to sort.
Remove unnecessary code.

- Refactor output of participants in overview mode.
    use get_participant_list of the participants themself.
- Remove comment for testing time output in the
    detailed view of conversations.
Move classes to lib directory.
Update main program to use classes from lib directory.
Add Gemfile.
Update .gitignore and add vendor directory to it.
Add data to Gemfile.
Update main program.

- Add Choice for passing command line options
- Add benchmark to get execution time
Update .gitignore for Gemfile.lock