v0.3.1-beta

This release fixes a few bugs. Here are some of the changes:

• Changing the starting sentence now resets your session so that you start immediately at the new sentence.
• Some changes were made to how the time left is calculated which should make it more accurate.
• Support for triangulation and single-language courses has been added. You can study multiple languages in one session or just listen to the sentences in your target language. This change paves the way for making more flexible courses in the future.
• The app should be better about updating the UI/current sentence playing when coming back to the study session page and there should be fewer issues (hopefully "none") starting multiple sessions without closing out of the app.
• Preliminary support for handling orientation changes.

NOTE: Upgrading to this version will erase your data/stats!