This is part of the multithreading journey. The parser and lexer were
using loads of global variables and all of these are now packed into
struct cf_context and others.
Note that the config API has changed:
* cfg_alloc[zu]?(size) is now cf_alloc[zu]?(ctx, size)
* cf_error(msg, ...) is now cf_error(ctx, msg, ...)
* config_parse() and cli_parse() are now called differently
* there is a brand new CF_CTX section in *.Y files which participates
in struct cf_context construction
