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
We set buffer->pos to buffer->end in function buffer_print() when
bvsnprintf() failed, so there would be uninitialized memory between
the old buffer->pos and the current buffer->pos.
Changes the time complexity of the algorithm from O(n^2) to O(n*log(n)).
This speeds up loading of huge DEC-IX config from 128 s to 15 s. It also
makes the code significantly simpler.
