Implement the known theoretical distribution L-moments

[jorenham]

distributions:

• cauchy()
• chi(2)
• chi(4)
• chi(6)
• expon() - Exact L-moments of several distributions #307
• gumbel_r() - Exact L-moments of several distributions #307
• gumbel_l() - exact L-moments for gumbel_l #351
• halfcauchy()
• halflogistic()
• halfnorm()
• laplace()
• logistic() - Exact L-moments of several distributions #307
• norm()
• rayleigh()
• t(1) (equiv cauchy())
• t(2)
• t(3)
• t(4)
• uniform() - Exact L-moments of several distributions #307

1-parameter distribution families:

• bernoulli(p=p)
• fisk(c=alpha) (equiv to burr(c=alpha, d=1) and burr12(c=alpha, d=1))
• genextreme(c=alpha) (GEV) - Exact L-moments of several distributions #307
• genpareto(a=alpha) (GPD) - Exact L-moments of several distributions #307
• gompertz(c=alpha)
• kappa4(h=-1, k=alpha) (GLO)
• lomax(c=alpha) (equiv to burr12(c=1, d=alpha))
• powerlaw(a=alpha)
• tukeylambda(lam=lambda) (equiv genlambda(b=lambda, d=lambda, f=0))

2-parameter distribution families:

• burr(c=alpha, d=beta)
• burr12(c=alpha, d=beta)
• kumaraswamy(a=alpha, b=beta) - Kumaraswamy's distribution implementation #112
• mielke(k=alpha * beta, s=alpha)

3-parameter distribution families:

• genlambda(b=beta, d=delta, f=phi) (GLD) - Generalized Lambda distribution implementation: distributions.genlambda #119
• wakeby(b=beta, d=delta, f=phi) - Wakeby distribution implementation #114