Included VB-logi method as one R-file. No extra dependencies.

Added the vb-fitter code in one R-file. 

Modifications to original code: 
* Extra parameter VB=FALSE in logi.engine 
* if-else in logi.engine to choose between glm and vblogit
* three methods for class 'vblogit', print, summary and predict, needed definition in NAMESPACE
No external dependencies.

Not the fastest right now but should work. All visible output is like using normal glm.