obsoleting old structures package in kForth

[Krishna Myneni]

I've decided to obsolete the older structures package in kForth, in
favor of using Forth-200x standardized data structures. The older
structures package is provided in

struct.4th

and the Forth-200x standard structures are provided in

struct-200x.4th

IIRC the origin of the older package is from Gforth.

Forth source programs in the kForth repos currently make use of one or
the other type of structures. Neither one is complete, in a practical
sense, making it necessary to add additional field specifiers for
unaligned fields, which is important for creating data structures
compatible with those used in external libraries. Thus, the kForth repos
also provide

struct-ext.4th

and

struct-200x-ext.4th

Over the coming months my aim is to modify existing code so that both
struct.4th and struct-ext.4th are no longer needed in the source code
provided in the kForth repos. The use of both kinds of structures, often
in the same program, is leading to confusion and difficulty in following
the source code.

--
Krishna Myneni