DOC: fix some spelling issues over multiple files
This is from the output of codespell and may be backported.
diff --git a/doc/internals/buffer-api.txt b/doc/internals/buffer-api.txt
index 14a1ac7..d4e26db 100644
--- a/doc/internals/buffer-api.txt
+++ b/doc/internals/buffer-api.txt
@@ -9,7 +9,7 @@
defragmentation, and are used to carry intermediary representations between the
various internal layers. They support wrapping at the end, and they carry their
own size information so that in theory it would be possible to use different
-buffer sizes in parallel eventhough this is not currently implemented.
+buffer sizes in parallel even though this is not currently implemented.
The format of this structure has evolved over time, to reach a point where it
is convenient and versatile enough to have permitted to make several internal