Phylo.root_with_outgroup: prevent an error if branch length is None
Phylo.to_networkx: docstring correction
Tutorial/Phylo: add another 'draw' example; mention RAxML wrapper
Phylo: fixed the bug in root_at_midpoint

Most trees don't have a branch length assigned to the root, so depths()
was ignoring this value without a noticeable problem. But when
root_at_midpoint() calls depths() on child clades, the leading branch
length should be included, at it wasn't.

Solution: include the root branch length in depths(). In
root_at_midpoint(), adjust the calculation of 'remainder' for the root
branch length since the root branch will not be traversed.
SearchIO._index cleanup
Bump version numbers for Biopython 1.60 release
Remove recently added but now unused compressed example files
Include BGZF examples
Include Tests/Graphics/README in manifest (need directory)
Tell git to ignore the generated MANIFEST file
Fix Hmmer parsers bug where there are no Hit descriptions (reported by Daniyal Kazempour)
More detailed error message in EMBOSS test
Add default value test for HSP objects
QueryResult and Hit descriptions are now properties affecting HSPs
Add new Fasta test cases
Add SearchIO fasta-m10 parsing and its tests
Add SearchIO fasta-m10 indexing and its tests
Add __str__ methods for common objects
Update parser's Hit and Query description set, to affect contained items
Add blat test cases