Fixed Extensions PKG in VHDL 2008 Back-Compatible Libraries

fixed_extensions_pkg is a fixed-point arithmetic package written in VHDL
according to the VHDL-2008 update of the standard. It uses VHDL-2008 back-
compatible libraries (by David Bishop) that are included in this distribution
for the sake of completeness.

Currently, the "fixed_extensions_pkg" package implements the following:

-ceil:
round towards plus infinity.
-fix:
round towards zero.
-floor:
round towards minus infinity.
-round:
round to nearest; ties to greatest absolute value.
-nearest:
round to nearest; ties to plus infinity.
-convergent:
round to nearest; ties to closest even.
-bitinsert:
bit-field insertion to word
-bitextract:
bit-field extraction from word

fixed_extensions is distributed along with a tool (gentestround) to generate
customized VHDL test designs.