$ZCODE_LESS_DICT_DATA option to omit last byte in dictionary words

[erkyrath]

Setting $ZCODE_LESS_DICT_DATA to a nonzero value tells the compiler to omit the last dict entry byte (the one referred to as #dict_par3). See #146 .

This turned out to be more of a pain than it looked. The Z-code dict computation of ((version_number==3)?7:9) was hardwired in quite a lot of places. I replaced them all with the DICT_ENTRY_BYTE_LENGTH compiler variable, which is set at startup time.

Complication: The Version directive can change the Z-code version in mid-compile, which means we must change DICT_ENTRY_BYTE_LENGTH at that point. And also the DICT_ENTRY_BYTES I6 constant. This is doable, it's just messy. See #147 about the idea of deprecating this directive.

Anyhow, with all that in place, we just have to reduce DICT_ENTRY_BYTE_LENGTH by one when $ZCODE_LESS_DICT_DATA is set.

We generate warnings and errors for three cases when $ZCODE_LESS_DICT_DATA is set:

• Warning when using Dictionary 'word' x y. (The third value is ignored.)
• Error when using #dict_par3.
• Error if you define verbs without using Grammar__Version 2. (GV1 wants to store the preposition number in the #dict_par3 field.)

[erkyrath]

https://github.com/erkyrath/Inform6-Testing/tree/small-dict (small-dict branch) has tests for this feature, including the errors and warnings.

Saves 728 bytes when compiling Advent.z5!