detach() to
  unload a package.
  If the package is not loaded, it will quietly return.## S3 method for class 'Package}(this, ...)':
unloadundefined
- ...{Not used.}
Returns nothing. 
pkg <- Package("boot")
  load(pkg)
  print(isLoaded(pkg))
  unload(pkg)
  print(isLoaded(pkg)) 
[object Object]
*load().
  *isLoaded().
  search().
  For more information see Package.internal 
methods