transferred functions from work in progress
noticed a missing article 'a' in a sentence
some doc changes
docstrings reviewed
some doc changes II, for some reason
Franco's suggestions
warnings added
copypaste oops
Initial version.
spelling according to Shareshian-Wachs
Merge branch 'master' into eulerian
the jackhammer approach to fixing the definition of dex
rest of the review
algorithms for trees and latex output

* several traversal algorithms
* some methods added for binary heap
trac #14498: some improvements on trees
trac #14498: Darij's review patch, to be applied ATOP of trac_14498-algorithms_trees-rebased.patch and trac_14498-tree-imps-dg-rebased.patch
trac #14498: more doc fixes
patch changes except for those in plot/animate.py
patch animate.py
allow user to override default png_dir; use tmp_filename for output, instead of graphics_filename