Various fixes for typos, conventions, nomenclature & corrections

The first argument to `install.packages()` is a library location, not a package. You can't update single packages with `update.packages()`, you can just install the package with `install.packages()`.

I also put the code example into a code block.

Changes in the second commit are mostly minor. Main change is to tweak how you refer to vectors and to simplify the way these are introduced, as in use `character()` not `vector("character")`. A number of other fixes/changes for nomenclature, consistency ect.