document boundary and other behavior

[RossBoylan]

It is unclear whether the boundaries are excluded/open or, if finite, included/closed in the set of values that might be generated by the random generator. While generating a random value at the boundary is highly unlikely, it would be nice to know if it is possible. I believe none of the other functions care, since a value at the boundary is an event of measure 0 and so won't affect the calculations.

The documentation is also not explicit about whether a and b are describing the region to exclude or include in the distribution.

Finally, the documentation says "Density, distribution function, ... for the truncated normal distribution with mean equal to 'mean' and standard deviation equal to 'sd'.". But the mean and sd in this case are presumably those of the untruncated normal distribution.