v0.3.0

Adds prefetch (preemptive caching) - Fixes #66
Sets default link selector to fetch all links except those with data-senna-off - Fixes #77
Should not trigger click event for the right mouse button - Fixes #58
An error should be issued if a surface element does not have an id - Fixes #56
Should check if attribute exists in order to throw error - Fixes #62
Removes child surface content after transition ends - Fixes #80
Makes app.createScreenInstance method public