Improve ToC and add missing section headings

Increase version to 0.6.0

`asoc-sort`: make comparator optional (default: `string<`), version->…

…0.5.0

Add "Maintainer" field and email address

Increase version to 0.4.5

Increase version to 0.4.4

Add `asoc-merge-values-no-dups` with docs, tests

Also, modify docstring example for `asoc-merge-values` to correspond to that
for `asoc-merge-values-no-dups`.

Increase version to 0.4.3.

Add `asoc-find` and `asoc--find` with docs, tests

Increase version to 0.4.2

Add `asoc-merge-values` function, with docs and tests

Increase version to 0.4.1.

Remove `keep-last` parameter from `asoc-uniq`, update docs & tests

The option to keep the last occurrence of a key is unlikely to be needed.
If it is, the alist can simply be reversed. Removing the option simplifies
`asoc-uniq`, making it equivalent to `asoc-merge` with a single argument.
It also leaves the option for expanding the interface later.

Also, update `asoc-merge` docstring and move `asoc-uniq` before `asoc-merge`.

Increase version to 0.4.0.

Add opt param `ignore-shadowed` to `asoc-values`, adjust docs/tests

Increase version to 0.3.5.