Adding new tinrc variables:

. Think of a name for your variable, we'll call it NAME
. Add it to tincfg.tbl, the ordering of this file decides the order of the
  Option 'M'enu. Use an appropriate type.
. Add an entry for it to the tin.1 manpage under the
  "GLOBAL OPTIONS MENU AND TINRC CONFIGURABLE VARIABLES" section
  and one to the tin.5 manpage under the "FILES" section (subsection tinrc)
. Add NAME with the correct type to the master declaration in tinrc.h
. Add an initial value for NAME in the correct position in t_config tinrc={};
  in init.c
. In config.c, add the following:

	In read_config_file(), a match_*() function to read NAME into the
	internal tinrc table, which may not necessarily be the same type.

	In write_config_file(), code to write out NAME in some ASCII
	friendly format.

	In change_config_file(), you may need an OPT_NAME: switch to do any
	special post-processing needed when NAME is changed on the Option
	'M'enu, particularly when using OPT_STRING

. Add the following definition to extern.h
	struct opttxt txt_NAME

. Fill the above structure out in lang.c
	help text  - shown as help when asked for in Option 'M'enu
	opt text   - the text shown on the left side in the Option 'M'enu
	tinrc text - the comment text that precedes the variable when
	             written to the tinrc file. This is optional.
