Add simpler Session constructor

Use DefaultMessageComparator by default.

Signed-off-by: Jussi Virtanen <jussi.virtanen@valotrading.com>
Take simpler Session constructor into use

Signed-off-by: Jussi Virtanen <jussi.virtanen@valotrading.com>
Remove Fields

It is not used by anyone.

Signed-off-by: Jussi Virtanen <jussi.virtanen@valotrading.com>
Merge pull request #127 from jvirtanen/features/simpler-session-constructor

Add simpler Session constructor
Merge pull request #128 from jvirtanen/cleanups/fields

Remove Fields