tag v0.6.1 release

Release pgx 0.6.0 (pgcentralfoundation#906)

0.6.0 alpha.2 prep (pgcentralfoundation#879)

* upgrade dependencies

* update version to 0.6.0-alpha.2

Release pgx 0.6.0-alpha.1 (pgcentralfoundation#871)

Some bugfixes and slightly improved error detection and docs, mostly!

Release pgx 0.6.0-alpha.0 (pgcentralfoundation#856)

bump to v0.5.6

Merge pull request pgcentralfoundation#808 from tcdi/0.5.5-prep

Release pgx 0.5.4 (pgcentralfoundation#802)

This release covers an incorrect handling of some Datum arguments,
some missed SpinLock macro bindings that we wanted to add to the C shim,
and introduces a base API for dynamic background worker registration!

Release pgx 0.5.3 (pgcentralfoundation#787)

This cuts pgx 0.5.3, which is mostly a bugfix release that covers a handful of
errors that had crept in to the end of the 0.5.0 test and release cycle.

Merge pull request pgcentralfoundation#770 from tcdi/0.5.2-quick

prepare for v0.5.2