v2.2.11—stay lit

2.3.0 is very, very close. Adds ncplane_erase_region() to erase a subregion of a plane. Adds ncblit_rgb_packed() and ncblit_rgb_loose() to blit RGBx and pure RGB. Fixes some flicker when using sixel. Fixes an error in sixel wiping. Relaxes an EGC test to WARN to pass on musl+s390x. Fixes notcurses-base.pc so that Requires.private specifies the proper source of Terminfo on the system, fixing static linking when libtinfo is built into libncurses instead of being a standalone deal.