Add feature subsetting to tree growth

These commits introduce Mtry (similar to RandomForest). Mtry is the
percentage of features to scan when creating the next node in the tree.

M number of features are tried at each node split. MTry is a percentage
which is converted into an integer.
Described changes

Added the description of the changes implemented in the feature
subsetting enhancement.
Create logic to do feature subsetting

This commit changes the spots to random choose a subset of feature to
test at each node.
Transfer the parameters from R to tree

These commits are necessary to transfer parameters from R to tree.cpp
where the feature subsetting is done.
Add feature subsetting parameter

Adds the parameter to the calls and objects to handle feature subsetting
during node creation.
Attempts to fix some errors

It appears to be an error with the CVs
Better checks and initialization of Offset

Offset was being passed to C++ a null and created errors. It was
retrieving erroneous data. This code replaces a NULL offset with a zero
filled vector.
Merge remote-tracking branch 'origin/Offset_Initialization' into feature_subset
Updated the Manuals to include mFeatures

The GBM and GBMCrossVal manuals were updated with mFeatures descriptions
and parameter listing.
Wrap up the mFeature parameter

Some language was wrong and some areas were commented out.
Updated some language and clear Rproj files

There were a bunch of unwanted RProj file to be removed and updated the
Change log.
Merge pull request #1 from Neil-Schneider/feature_subset

mFeature Parameter