Plug a few possible small memory leaks
Autotools: enable Automake warnings
Autotools: always put object files in the source file's directory

Enable Automake option "subdir-object" to put all object files next to
their source file rather than in the directory containing the Makefile.

This is quite expected, and will be the future behavior of Automake in
all cases, so enabling it now avoids future unexpected change.
Autotools: fix building the documentation in VPATH builds
Autotools: use the target file as the base rule for building documentation

This allows automatic building of the file when required, and allows
user to request building that specific file.
Fix a typo in the documentation's markup
Fix truncation of the data retrieved with --list-documents

Do not truncate the document list to the size of the buffer used for
communication.

Since we now read multiple times, we need to make sure to always send
ETX so a reader don't hang reading the next chunk if the data sent had
exactly the size of the buffer.