v0.31.1: one button look — crisper emboss, darken on hover

- The emboss hugs the edges: thin lit and shaded rims, a defined outline
  that's a touch darker along the bottom, and a nearly flat face — shape
  without depth.
- Hover darkens the whole button slightly instead of Qt's pale panel on
  top of it.
- One face for every button (theme.button_face_qss): regular buttons,
  Library and its ▾, the purple friend-mode buttons, and the transport
  boxes. Shuffle and bpm are boxes that are one button, so the whole box
  darkens (bpm's whole box is now its tap target); the play box's three
  tiles each darken on their own.

lintunes/__init__.py

@@ -1,3 +1,3 @@
 """LinTunes — iTunes-style music library manager and player for Linux."""
 
-__version__ = "0.31.0"
+__version__ = "0.31.1"