1.9.13 `distance` adds "wunifrac" option.

Merge branch 'pr/384'
CHANGES IN VERSION 1.9.13
-------------------------

USER-VISIBLE CHANGES

	- `distance` function now supports "wunifrac" option, for
`UniFrac(..., weighted=TRUE)`

	- `distance` function regexpr-matching for range of variants for
weighted-UniFrac, unweighted-UniFrac method option

	- `distance` function regexpr-matching for `type` argument range of
alternatives

	- Proposed in https://github.com/joey711/phyloseq/pull/384