auto-compile-toggle-mark-failed-modified: remove unused argument
auto-compile-byte-compile: show error about unbalanced parens
fix section nesting

"Toggle and Perform Compilation" is not a subsection of "Options".
optionally add warning counter to mode line

as an alternative to automatically displaying the *Compile-Log* buffer
when there are warnings.  Add new options `auto-compile-display-buffer'
and `auto-compile-mode-line-counter' to control the behavior.  Setting
the former to nil and the latter to t makes the automatic compilation
less intrusive.
add auto-compile-inhibit-compile-hook

to allow inhibiting automatic compilation under user-defined
circumstances.

Also add `auto-compile-inhibit-compile-detached-git-head' but do
not add it to the hook variable's default value.

Start using `cl-defun' to define `auto-compile-byte-compile' and
then use `cl-return-from' to abort compilation when the hook succeeds.
This avoids having to reindent the whole thing.
add Makefile
improve library commentary

Make it shorter and concentrate on the things users actually need to
know.  Most importantly mention the new options that can be used to
make automatic compilation less intrusive.
add README.md

Add a rule to the Makefile to generate README.md from the library
commentary in the library.  Track the generated file.
check whether auto-compile-file-buffer is non-nil before use

Auto-Compile isn't the only one triggering compilation.  When
something else does it, then `auto-compile-file-buffer' is nil.