Move rbenv path outside if statement

Commit 0c3d21a placed the initialization of rbenv, including exporting
its path, in an if statement. Since the rbenv path was exported inside
the if statement, the if statement always failed. We solve this by
moving the path line only outside the if block.
Quickly go to beginning and end of history

Sometimes we get "stuck" in the history, i.e. when searching through the
history then clearing the line. fn + up or down arrow now brings us to
the beginning or end of the entire history.
fn + backspace should work as the delete key

Pressing fn + backspace should work as the delete key: delete the
character below the cursor, not insert a tilde (~) as they for some
reason did.