1.0.1 - Render crash hotfix / notes about filepaths

This is a quick patch to address some crashing and other misbehavior during song Render. (Thanks to @sodapop67 for reporting this.)

Here are the patch changes:

• Fixed a bug that was causing unpredictable crashes during song render. (Please let me know if you run into any more render crashes using 1.0.1!)
• Fixed a bug that was trimming the last character off the names of some rendered songs.
• The Render button will now change its label to "Cancel" while rendering is in progress, and pressing it again mid-render will now properly cancel the render.

I also have a couple notes on how saving/rendering works right now in Pebble.

You can either type a full filepath in the FILE bar, or just a file name. If you don't specify the full path, saved files are going to end up in the same folder as your Pebble executable. If you're using the itch launcher, that will be wherever the launcher is set to install apps. You can look that up in your itch settings, as it varies by operating system.

When you render a song, the resulting WAV file will be saved to the same folder as its source file, so it will also end up alongside the executable if no path is specified.

It's also worth noting that when you click Save, Pebble will save to whatever is currently in the FILE bar. So if you load a file, change the FILE bar, and click save, you will essentially be doing a "Save As".

One of my main goals for the next version is to add some file selection windows and other UI tweaks to improve the saving/loading aspect.