docs: mic meter demo

[nathanbabcock]

Capture audio from the mic with FFmpeg and visualize volume levels in real time via ASCII rendered to the terminal.

TODO

• Add a more convenient .inspect_errors() function to the core iterator for debugging purposes
  • Iterator helper methods like inspect_errors() #66
• Prevent log message events that only contain a single newline from FFmpeg logs
• Fix bug in chunked output mode that prevents it from reading audio-type outputs + add test