Minor changes to documentation

I made some minor changes to the code documentation:
* foxed some typos in the vignette bibtex file
* added a few more code comments, especially connecting the code to the explanations in the vignette
* used @slot tag in class definition
* used \linkS4class for links to classes
* added a few more @param tags
* fixed some typos
* wrapped some very long comments
These are unimportant, but they also do not do any harm, so i thought I'd share them just in case you feel like merging them in. These changes do not yet address the warnings one gets when compiling the documentation files with the current version of roxygen2.

I will continue to commit changes to the vignette and the code documentation to this branch as I dive deeper into mizer.