Little corrections

Hi,

I am a student at the University of Padua, of Land and Environment Science and Technology course.
I’m interested in growth model for woody crop, and I'm studying the program PCSE.

I have found some bugs, mainly in the PCSE documentation.
For my consideration, there are two errors in the code, about call of variables.

I hope that my contribution has been helpful.
Sincerely,

Ivan Orzan