Support high-resolution stats; add audio stats framework

[andygrundman]

NOTE: this patch depends on a patch to moonlight-common-c, see this PR.

• Adds an audio stats overlay that works with all current renderers, showing common info such as bitrate and packet loss. It is blue and in the upper-right, and will appear whenever the video overlay is enabled.
• Audio renderers are able to add more lines to the overlay (the upcoming CoreAudio patch uses this).
• Added bitrate/FEC display to both video and audio stats.
• Consolidated the 3 FPS lines into one to save a bit of space.
• All time-based stats are now microsecond-based, improving accuracy of very fast events.