change "tsolvepd" into "toepsolpd", update Changelog and write documentation
add tsolvepd funciton
save a few CPU cycles
fix a bug in which() (vector case)
implement calculation of "fixed-effects" in fols (not exposed to the user level yet)
document the new functions for the truncated normal distribution
allow series argument for truncated normal generation
add cdf and pdf for the truncated normal distribution