databases/tinycdb: Update to 0.81

- Update manpage location (003a571d, r523104)

Changes:
 - ship simple libcdb.pc (install it to pkgconfdir=$(libdir)/pkgconfig)
 - to avoid further questions, change license from "Public domain" to MIT
   license, add copyright and license text to all source files.
 - change default compiler optimization level from -O to -O2, use gnu tar
   --transform option to create dist archive, other small changes to Makefile