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 man page under the
  "GLOBAL OPTIONS MENU AND TINRC CONFIGURABLE VARIABLES" section
  and one to the tin.5 man page under the "FILES" section (subsection tinrc)
. Add NAME with the correct type to the main declaration in tinrc.h
. Add an initial value for NAME in the correct position in t_config tinrc={};
  in init.c
. In config.c/options_menu.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
	             should be 80 characters max
	opt text   - the text shown on the left side in the Option 'M'enu
	             should be 36 characters max, including the tailing :
	tinrc text - the comment text that precedes the variable when
	             written to the tinrc file. This is optional.

. If the variable is to be chosen from a list, then the second field of
  tincfg.tbl is the name of an array which holds the textual descriptions
  of the options. Add this array to lang.c and extern.h
  Don't forget to add NULL as the very last array member in lang.c. Various
  functions rely on it.

Adding a new attribute:

. Think of a name, we'll call it NAME
. Document it on the tin.5 man page under the
  "${TIN_HOMEDIR-"$HOME"}/.tin/attributes" section
. Add it to the t_attribute and t_attribute_state structure in tin.h
. Define the default value for it in attrib.c:set_default_attributes()
. Set the default state for it in attrib.c:set_default_state()
. Add it to tinrc.h and tincfg.tbl
. In read_attributes_file() add a MATCH_<TYPE> entry to parse it in
  under the appropriate first letter section.
. In set_attrib() and assign_attributes_to_groups(), add a corresponding
  SET_<TYPE> entry
. In write_attributes_file(), add a minimal entry in the header to
  describe the usage of the attribute and add code to write out the
  attribute
. In skip_scope() add code to check if the attribute is set
. Add code to write out the attribute in dump_attributes() and dump_scopes()
. In options_menu.c:config_page() add UPDATE_(INT_|STRING_)ATTRIBUTES
  under the appropriate case OPT_* section; add entries in option_is_visible(),
  check_state(), reset_state(), initialize_attributes()
. Free up the attribute in memory.c:free_attributes_array() if needed

Where possible try to keep the ordering of the attributes in the various
functions and structures consistent