Merge branch 'release/0.2.1'
Enhance error message
Fix typo
New failing specs
debugger gems
TagTree::Node#last_non_empty_node
Merge branch 'develop' into hotfix/prev_of_first_leaf
Version bump to 0.2.2
Merge branch 'hotfix/prev_of_first_leaf'
Merge tag 'v0.2.2' into develop

Version 0.2.2

 * Fix #prev of the first leaf with an empty node