databases/tinycdb: Update to 0.81

• Update manpage location (003a571d1d6585196545295efc181514f171c4c4, 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