create magic comment "whofield" for id fields of non-core macros

Although we can now auto-recognize characters in the core NAMED_*UNIT macros,
campaigns may have their own recruit/recall macros. This comment will tell
wmllint which field contains the macro's id.

The basic format is 'wmllint: whofield <macro> <num>'. This commit sets up the
dictionary, the next commit will actually parse the macros. It will explain
more details about how to use this magic comment in wmllint's introduction.
parse whofield macros to recognize unit id fields

Also, explain usage of the "whofield" magic comment in the introduction
add RECALL to core unit macros

Many UMC projects already have a RECALL macro.
add RECALL_XY macro to core

Many UMC projects have a macro for this function, but the name isn't
standardized (RECALLXY and RECALL_POS are also in use). However, regardless
of name, all these macros follow the "id x y" order, so for compatibility
I have kept that order. UMC authors started with a RECALL macro and added
coordinates, while the unit-generating macros have to organize a lot of
extra fields that are irrelevant to [recall].
NR 05a - The Pursuit: add dialogue when a unit steps on the dungeon signpost

Most of the other signposts elicit a remark when a unit steps on them, but
curiously not this one.

Not only do I give the discovering unit a line, I have Tallin speak as
well. This may give alert first-time NR players a clue that this corridor
is important.

Some may prefer that players continue stumbling about, and object.
Unfortunately, there's no NR maintainer or active lord of prose to resolve
any difference of opinion.
wmllint: recognize characters in RECALL_XY
THoT Dwarvish_Loremaster: fix typo in apparently unnecessary magic comment

The irony of turning off spellcheck and misspelling spellcheck is obvious.

This magic comment is apparently unnecessary, though, since it wasn't
working, yet the file was not failing the spellcheck.
update changelog with my recent contributions