More typo fixes across the tree

Previously I have made spelling changes as caught by Debian's lintian
tool, which has a short list of common misspellings that it tests for.
This time I decided to run codespell against the source and fix all the
obvious problems it came up with. It also uses a list of misspellings
but it's much larger than lintian's, but also has some false positives
so I went over the list by hand.

The command I used to do check the source was:
git ls-tree -rz --name-only HEAD | xargs -0 codespell -L minimise,errorstring

audio.c

@@ -157,7 +157,7 @@ void parse_general_audio_options(void) {
       }
     }
 
-    /* Get the minumum buffer size for fancy interpolation setting in seconds. */
+    /* Get the minimum buffer size for fancy interpolation setting in seconds. */
     if (config_lookup_float(config.cfg,
                             "general.audio_backend_buffer_interpolation_threshold_in_seconds",
                             &dvalue)) {