Update NEWS.
doom: Add -pack parameter to specify mission pack.

The main purpose for this parameter is to allow mods made for the Final
Doom IWADs to be played properly with Freedoom. Chocolate Doom detects
mission packs (pack_tnt/pack_plut) based on the file name. However, the
Freedoom: Phase 2 IWAD contains the textures for all three Doom2-format
IWADs, so can be used to play MegaWADs like Plutonia 2 that were
designed to be played with plutonia.wad.

Because mission pack detection is done based on filename, freedoom2.wad
is handled the same as doom2.wad (a sensible default). But this means that
when playing using a mod like Plutonia 2, the wrong level name is shown
on the automap screen (along with eg. intermission text). To fix this we
need a way to manually override the mission pack. -pack allows this to
be done. It's kind of tedious that this has to be done manually but at
least it can be done.

Thanks chungy for the bug report/suggestion. This fixes #449.
Merge branch 'master' of github.com:chocolate-doom/chocolate-doom