Aravis 0.8.21

• build: FreeBSD support #620 (Rim)
• gigevision: performance improvement of standard socket method #617 (Emilio)
• usb3vision: prevent USB command mix up #622 (Edgar)
• usb3vision: fix PacketResend size field in extended ID mode #642 (Alexander)
• genicam: allow more Category child nodes #632 (Emmanuel)
• genicam: AccessMode fixes #634 (Emmanuel)
• genicam: fix pIsLocked when target is a Boolean node #638 (Emmanuel)
• doc: port to gi-docgen #621 (Emmanuel)
• git: default branch is main now (Emmanuel)