improvements to p_setup.c

- added extensive comments indicating code changes introduced by
  adding support for extended nodes and removing the BLOCKMAP limit
- refined and moved some other comments
- adjusted the conditional for clearing the ML_TWOSIDED flag for lines
  with no second linedef. none of the variables checked for in
  (singleplayer) are set correctly when the maps are loaded, so
  explicitely check the commend line parameters instead. yes, this is the
  fix fixing the fix. :)
improvements to g_game.c

- added and refined comments
- revert the fist being selectable when the chainsaw is equiped,
  this is demo critical, part one to remove this feature on the way to
  "Back to the Roots"
- moved decision about colored text into the text rendering routine
  (commited later)
- revert the chainsaw being selected when starting a new level, this
  is demo critical, "Back to the Roots"
- revert white space change relative to Chocolate Doom
- avoid code duplication for clearing the "savename" variable
- not pressing the "run" key when resurrecting will now start the
  level from scratch, this is the reverse behaviour for that feature
  but closer to Vanilla, "Back to the Roots", keep the (singleplayer)
  conditional since this somehiw affect "progression"
- minor coding style adjustments
improvements to m_menu.c

- added and refined comments
- correctly initialized boolean variables
- do not unconditionally set "dp_translation = NULL;" anymore
- corrected some indentation
- made G_ReloadLevel() and G_GotoNextLevel() static
- added an additional "else" between two contradictory "if"s
- treat G_ReloadLevel() and G_GotoNextLevel() as shortcuts to the
  IDCLEV cheat and thus add (!netgame) conditionals
improvements to hu_*.c

- added and refined comments
- fixed indentation in HUlib_drawTextLine()
- do not include v_video.h and p_local.h anymore, instead declare
  "extern byte *dp_translation" and "extern fixed_t P_AimLineAttack"
  and "extern mobj_t* linetarget"
- do not unconditionally set "dp_translation = NULL" anymore
improvements to p_*.c

- add and refine comments
- clarify origins of code snippets
- fix indentation
- Back to the Roots:
  - unconditionally randomize corpse health, this is considered
    harmless
  - do not vertically bob ammo anymore, this has been proven to
    potentially desync demos
  - do not add extra damage to the lethal pellet of a point-blank SSG
    shot anymore, this causes demo desync anytime it happens, do not
    include p_local.h anymore, do not declare "boolean
    P_CheckMeleeRange" anymore
  - Lost Souls now unconditionally bleed Puffs, this is considered
    harmless
  - the paradox "if (!player->weaponowned[player->readyweapon])" case
    is now checked for unconditionally, should only be relevant when
    removing the current weapon with the TNTWEAPx cheat
  - the weapon sprite is now unconditionally centered horizontally
    when shooting, vertical position is left untouched as this affects
    weapon lowering and raising and thus desyncs demos
  - remove possibility to toggle fist and chainsaw, not possible in
    Vanilla and likely to desync demos
  - since this already covers most of the "Back to the Roots"
    campaign, this commit fixes #31
- correnctly check and set boolean variables
- the "P_ThinkerToIndex()" and "P_IndexToThinker()" functions have
  been moved some lines up in src/doom/p_saveg.c, made static and
  removed from the header file, the "restoretargets_fail" variable has
  been made static
- re-add but comment out clearing of mobj->target and mobj->tracer
  fields in P_UnArchiveThinkers()
- the HUSTR_SECRETFOUND definition has been moved to rc/doom/p_spec.c,
  the only splace where this is actually needed, the "dstrings.h"
  header is thus not included from this file anymore
- very long lines have been split
improvements to r_*.c

- add and refine comments
- indicate origin of R_DrawColumnInCache(), R_GenerateComposite() and
  R_GenerateLookup() implementations, add copyright header
- do not include v_trans.h anymore, instead declare "extern byte
  *tranmap"
- indicate origin of R_DrawColumn() implementation, add copyright
  header
- do not include v_video.h anymore, instead declare "extern void
  V_DrawFilledBox()"
- check for "if (setblocks >= 11)" instead of "== 12", who knows what
  comes next ;)
- make "R_RaiseVisplanes()" static
- fix indentation for a smaller white-space delta with Choco
- remove the singleplayer check from the sprite flipping decision
  ("Back to the Roots"), flip barrel explosions again (why not, again?)
fix crashes with IDMUS

specifically prevent crash with IDMUS00 in Doom II and
with IDMUS0x or IDMUSx0 in Doom

fixes #34

also, fix/add comments and declare "extern boolean P_CheckAmmo()"
where it is actually needed
more code improvements

I think with this commit I have reached a point where I have
- properly commented and documented my code changes and my own code
- made new global variables and functions static where possible
- avoided the unnecessary inclusion of headers
- kept the white-space delta to Choco at a minimum

This commit thus fixes #30
avoid code duplication when setting "dp_translation = NULL"
introduce a better check for clearing the ML_TWOSIDED flag from single-sided walls

actually, this is fixing the fix for the fix ;)
ignore un-pausing in menus during demo recording
duplicate for-loop for the (dp_translation != NULL) case

to avoid checking that variable for each pixel and instead check once per patch

also, flipped patches are never color-translated
implement key_alt_* and unbind menu keys from movement

fixes #35