GUAC-608: Change semantics of clipboard instruction within libguac.
GUAC-608: Implement outbound clipboard streaming. Stub out inbound.
GUAC-608: Add common clipboard code.
GUAC-608: Migrate RDP to common clipboard code for outbound data.
GUAC-608: Migrate RDP to common clipboard code for inbound data.
GUAC-608: Make guac_iconv input const.
GUAC-608: Migrate test to non-clipboard instruction.
GUAC-608: Convert VNC outbound clipboard to common code. Stub inbound clipboard.
GUAC-608: Add inbound clipboard. Remove use of iconv().
GUAC-608: Add support for outbound clipboard for SSH. Partial inbound support.
GUAC-611: Add per-stream handlers for ack/blob/end. Simplify ack/blob/end contents. Reorganize headers to eliminate circular dependencies.
GUAC-611: Add missing headers.