- The core clustering code has been completely re-written and is
now far more efficient. - 
- Clustering is typically about ten times faster now.
- Due to changes in how chi-squared calculations are now made and
combined clusters are tracked along the way, potential row combinations
that are “tied” (or have chi-squared reductions that are so extremely
close as to be essentially tied) may be clustered in a different order
compared to the version 1.0 function.
- This generally only affects earlier clustering steps, well above
where most cut points will be in practice.
- If results from a previous version 1.0 clustering need to be
reproduced exactly for every step, you can force the use of the old
function by calling greenclust:::.greenclust.v1(). This
feature is not guaranteed to remain in future versions.
 
 
- Verbose output now includes the names of the two rows that were
combined at each step. 
- Fix for passing data frames to - greenclust()(#8)