Minor feature release

Minor feature release, providing a tree distance metric and various method to manipulate tree sequence data.

New features

• Kendall-Colijn tree distance metric computed by Tree.kc_distance (@awohns, #172).
• New “timeasc” and “timedesc” orders for tree traversals (@benjeffery, #246, #399).
• Up to 2X performance improvements to tree traversals (@benjeffery, #400).
• Add trim, delete_sites, keep_intervals and delete_intervals methods to edit tree sequence data. (@hyanwong, #364, #372, #377, #390).
• Initial online documentation for CLI (@hyanwong, #414).
• Various documentation improvements (@hyanwong, @jeromekelleher, @petrelharp).
• Rename the map_ancestors function to link_ancestors (@hyanwong, @gtsambos; #406, #262). The original function is retained as an deprecated alias.

Bugfixes

• Fix height scaling issues with SVG tree drawing (@jeromekelleher, #407, #383, #378).
• Do not reuse buffers in LdCalculator (@jeromekelleher). See #397 and #396.