Add support for tree agglomeration
Add missing rename_node function
Bug fix: mistyped 'qitem' instead of 'qlink'
Update tests for tree agglomeration
Add function to remove merged boundaries
Remove merged boundaries when getting segmentation
Major bug fix: peek only at valid queue items

MergeQueue.peek() was designed to look at the next item in the merge
queue without popping it. However, the next item *could* be invalid,
and cause a merge of a valid item past threshold!

This commit fixes that by having peek() discard invalid items until a
valid one is at the front of the queue.
Change feature testing to use update node ids
Update RIG creation to use watershed, not segmentation
Update refine_post_merge_boundaries to use tree agglo
Bug fix: reset tree height after ladder agglo
Change call order for tree merge

Tree merging was causing the sp2segment map to be incorrect when the
merge boundaries were being refined. Postponing the merge until after
boundary refinement fixes the issue.
Update contingency table to allow sequential node renaming
Update tests to allow 1-1 matching of segmentations
Update region intersection graph during merge

The region intersection graph allows quick computation of current VI
and rand index during an agglomeration run.
Update requirement to viridis 0.2
Update README.md

Adds Janelia Logo to README
Add missing argument to classifier_extension function
Merge pull request #35 from jni/ext-fix

Add missing argument to classifier_extension function
catch deprecated Image library import method

should work for both python-pillow and python-imaging