Update NEWS with all of the changes since last release

Change the version to 0.23. There are enough changes that it warrants
a minor version bump.

Signed-off-by: Enji Cooper <ngie@FreeBSD.org>

atf_check: fix std::length_error thrown from temp_file

The previous logic used 2 separate calls to `atf::fs::path::str()` when
constructing a `std::vector<char>` to pass to `mkstemp(..)`. This in
turn caused grief with how data copying is done in atf-c(3), etc, as the
prior code computed the length of the path of an internal buffer in
`atf_dynstr` structs.

Moreover, the code was manually appending a nul char, which was
unnecessary when making the valid assumption that `std::string` is a
nul-terminated string.

The new code convert the path to an `std::string` once, includes the
existing nul char in the buffer, then passes it to mkstemp(3) instead.
The code works properly now.

Closes:	#76
Signed-off-by: Enji Cooper <ngie@FreeBSD.org>

Add release date for 0.22

Release atf-0.21

Update release notes accordingly and bump the major version of the shared
libraries.

In theory, bumping the major version is not strictly necessary because we
only removed the internal config module... but there might be binaries out
there relying on it (see the old version of the ATF libraries in NetBSD).
Better be safe than sorry given that a symbol removal requires a major
version bump.

Release 0.20

Release 0.19

Set release date for 0.18 to today

Update release notes for 0.17

Set release date of 0.17 to today and format the notes properly.

Formal release tag for atf-0.16

Formal release tag for atf-0.15