Mark `print` as exported
Simplify installation

Fully qualify `install_github` installation so that the code works out-of-the-box, without having to load `devtools` first.
Merge branch 'develop'
Update documentation
Only import operators if there are any
Simplify module and operator attachment code
Patch .Rprofile
Add test cases for detach on unload
Detach modules when unloading them
Fix redundant unload in old test
Reattach modules correctly when reloading
Merge branch 'detach_on_unload' into develop

Resolves #27.
Merge branch 'develop'
Update documentation