[do not merge] Skip internal underflow

[patricksurry]

Here's work in progress that adds w_ labels. Also:

• some improvements for #;
• simplifies return stack operator compilation (removes strip-table checks with new ST flag);
• moves and simplifies headers.asm with def_nt macro;
• shortens s_quote by moving lookup table outside word;
• adds words/README.md;
• fixes #96

[SamCoVT]

I think this looks good so far. You're welcome to include results.txt (I'll clean it up if it makes a mess when merging) as it may show improvement just in the words that already have cycle tests (+/- the normal cycle test deviation due to addresses crossing pages).

[SamCoVT]

I think they shouldn't have the code field flag. I was trying to do them as deferred words, but it's really difficult to do that in ROM. I believe the current solution is that these are all helper words that use the actual vector held in RAM in the system variables (not sure if it's in the ZP variables or the RAM variables). I suspect this is a documentation error (eg. the comment is wrong) for the way things are currently done.

[patricksurry]

i'm going to split this up into smaller parts to make it easier to review

[patricksurry]

Split into #106 #107 and #108

I'll add one more with just the w_ label changes and then close this

[patricksurry]

109 now has just the original xt to w changes, without any header macro-izing. I'll explore that separately.