Created getstr_offset property (mirrors sbbs_t::getstr_offset value).

Created beep() method to send beep characters to remote console.
ansi_gotoxy() method now accepts a single object argument with x and y
properties (like that returned from ansi_gotoxy), or separate number arguments
for x and y values (as before).
All ansi_* methods now have aliases without the ansi_ prefix, in preperation of
supporting other (non-ANSI) terminal emulations in the future.