Add functions to get information on what the player knows from an item

[takkaria]

This is so some particularly ugly string-parsing functions can be removed from the Borg and it can be a lot more streamlined. As long as the UI uses the same functions, there is no information leakage. (I don't subscribe to the idea that the Borg should work by reading the screen, since I want a Borg to work even if I'm on the DS with a non-standard screen setup, or using OpenGL to render the game in perspective.)

For the kind of code it would help replace, see ​http://repo.or.cz/w/angband/borg/takk.git?a=blob;f=src/borg3.c;h=1eed6f205a22cf567ea74d2a3e7a2c6da24a2ddb;hb=HEAD#l1632

[magnate]

See also #749

[magnate]

Done with the changes to identify.c in 3.1 and 3.2