Add playback plus improvements to logging and merge of cpp client

This PR does the following:

 * Bug fixes and edits to mongodb_log to ensure it's working as desired
 * Added a node to playback topics recorded by mongodb_log, fixing #5 
 * Merges cpp client into the main package fixing #91 and #95 

Tests and documentation still to come, but putting this up for Jenkins to have a look at at least.