Annotate doco re-org

[Andrew Cagney]

I guess I get to re-vamp the annotate doco.  I'd like to do it as follows:

- verbatim insert the existing contents of doc/annotate.texi into 
gdb.texinfo, but _after_ the MI chapter.

- change the old doc/annotate.texi file into a standalone quick 'n' 
nasty migrating to MI document.  Would contain commentary explaining 
problems with various annotate #2 features and what their equivalent is.

- rewrite the annotate chapter (now part of gdb.texinfo) to reflect 
annotate level #3.

Thoughts?

Andrew