Buffer increase (aptly-dev#738)

Increase Scanner buffer size for Stanza reader

Merge pull request aptly-dev#683 from smira/545-download-contxt

Use Go context to abort gracefully mirror updates

Merge pull request aptly-dev#614 from smira/600-fix-double-mirror-update

Fix bug with `PoolPath` field being overwritten on mirror update

Merge pull request aptly-dev#613 from smira/607-trim-slashes

Trim slashes while parsing publish prefix

Fix temporary contents DB being left behind after publishing

NB: Go `defer` order execution is reverse to the order `defer` statements
are executed.

So before the change, `Drop()` was called before `Close()`, which was no-op.

Change that to explicit order in single func, print errors if they happen.

Merge pull request aptly-dev#531 from smira/release-1.0.0-preparation

Prepare for new release, update build instructions [ci skip]

Release 0.9.7.

Fix one more system test on version.

Version bump to 0.9.5.

Version bump to 0.9.1