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

tinyhttp/chunk.h

@@ -33,7 +33,7 @@ extern "C" {
 
 /**
  * Parses the size out of a chunk-encoded HTTP response. Returns non-zero if it
- * needs more data. Retuns zero success or error. When error: size == -1 On
+ * needs more data. Returns zero success or error. When error: size == -1 On
  * success, size = size of following chunk data excluding trailing \r\n. User is
  * expected to process or otherwise seek past chunk data up to the trailing
  * \r\n. The state parameter is used for internal state and should be