migration to IterativeSolvers, bug fixes, increased coverage

Author: SebastianAment

Project.toml

@@ -4,6 +4,8 @@ version = "0.7.0"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"
+DSP = "717857b8-e6f2-59f4-9121-6e50c889abd2"
+IterativeSolvers = "42fd0dbc-a981-5370-80f2-aaf504508153"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 StatsBase = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"