Installing and using an R package from a custom folder

On some computers you can't install new packages for R in the 'library' folder because of security considerations on Windows machines. Here's an explanation on how to use custom directory to install the package and still be able to use it using the library() function: http://users.fmg.uva.nl/rgrasman/R_LIBS.html
The simpler way is to specify the lib.loc parameter in library, but the way presented here is more convenient when multiple libraries are used or just tried out under these circumstances.