Started new gadget processing code for gadget_excise.
Created new gadget read/write routines and added gadget_excise.
Fixed a bug in the pcounter code.
Very large commit (I know ... I know ... new workflow, ok?!), mostly to support more merger tree analysis tools.
Added accretion history merger tree analysis code.
Added code for buffering SID_fread_all and applied it in compute_accretion_analysis().
Improvements/bug fixes to handling of treenode markers for groups.
Completed integration of treenode marker analysis.
First histogram code introduced and implemented in gbpTrees (make_trees_markers).
Created a new directory for histogram functions (gbpHist).
Moved histogram tend material from make_trees_markers to gbpHist.  Created gbp_va_list routines for this purpose.
Split creation and writing of markers off from tree analysis.  Created the executable 'make_trees_analysis_relaxation'.
Switched marker reading to marker precomputation in make_trees_analysis_relaxation.
Created init_treenode_trend* wrapper functions for gbpTrees.
Added functionality to gbpTrees analysis and gbpHist.