* implement procedure of MSDO/MDSO in p29

* undocumented functions include findParsimonious, overlap, which.commonConfiguration.

* plot method for QCA object with aids from Vennerable packages.

* Can use gtools to improve speed of solvePIChart(), but not use it until necessary. The other option is to use commbinations in omegathat or use Rcpp to use C++ code instead of R code.

* handle necessary conditions.

* examine the logical relation between the derived variable and original variables (for TQCA).
