crc_table is made using a four-byte integer (when that can be
determined).  However get_crc_table() returned a pointer to an
unsigned long, which could be eight bytes.  This fixes that by
creating a new z_crc_t type for the crc_table.

This type is also used for the BYFOUR crc calculations that depend
on a four-byte type.  The four-byte type can now be determined by
./configure, which also solves a problem where ./configure --solo
would never use BYFOUR.  No the Z_U4 #define indicates that four-
byte integer was found either by ./configure or by zconf.h.

The conversion to multi-byte will be locale-specific, but it's
better than nothing and is only to provide more information in the
error message returned by gz_error().  The conversion has no
effect on what's opened.

Also need to #include <stddef.h> for zlib.h, and need to workaround
the inability to use wide characters in constructed error messages
with zlib's interface.

	modified:   CMakeLists.txt

Add a version variable so it gets added to the pkg-config file.

Using optimized byte swaps reduced portability for no real benefit,
since they are in parts of the code that represent a tiny fraction
of the execution time.  So a simple definition of a byte swap is
now used.