MAINT: stats: Use explicit formulas for the mean, variance, skew and kurtosis of the loggamma distribution.
TST: stats: Add a test for the loggamma distribution stats.
STY: stats: fix line length
MAINT: stats: micro-optimization in loggamma stats method--reuse the value of var
Merge pull request #2548 from WarrenWeckesser/stats-loggamma

MAINT: stats: Use explicit formulas for the loggamma stats.