grunwaldlab/poppr: Poppr version 2.8.3

This version of poppr has a bug fix, a much-needed improvement to the display of single-population nodes in MSN (by @fdchevalier), and minor changes to stability that should not be noticed by users.

The new MSN no longer draw the single-population nodes as a pie, so they look more presentable

I also accidentally forgot to include the NEWS file in the official release, but you can still keep track of that here:

• read.genalex() now correctly parses strata when the user imports data that contains duplicated data AND has some individuals named as integers less than the number of samples in the data (prepended by zeroes) (See https://github.com/grunwaldlab/poppr/pull/202).

• MSN functions: nodes with single populations displayed as circles instead of pies. (@fdchevalier, https://github.com/grunwaldlab/poppr/pull/203)

• mlg.vector() is now safer as it now uses a for loop instead of a function with the out-of-scope operator (<<-) (see #205)
• shufflepop() is now safer as it now uses a for loop instead of a function with the out-of-scope operator (<<-) (see #205)
• The MLG class gains a new distenv slot, which will store the environment where the distance function or matrix exists. This is accompanied by an accessor of the same name (see #206).
• "mlg.filter<-"() replacement methods will no longer search the global environment when evaluating the distance function or matrix (see #206).
• Tests for mlg.filter() no longer assign objects to the global environment
• DOIs for the publications have been added to the DESCRIPTION