(svn r6925) -Codechange: Be more strict with widget distinctions. WWT_PANEL is only plain panel,
WWT_IMGBTN must contain an image for drawing. Renamed WWT_PANEL_2 to WWT_IMGBTN_2
because that is what it is. Added WWT_PUSHBTN that is either just a pushable button,
or a textbutton, which text's drawn dynamically independent of widget.

(svn r5918) -Cleanup: rename ConvertDayToYMD/ConvertYMDToDay as they really convert a Date to/from a YearMonthDay.
-Cleanup: swap ConvertDateToYMD's parameters to make the order consistent with the name of the function.

(svn r5887) -Cleanup: move date related functions, defines and variables to date.[ch]
-Cleanup: fix whitespace related coding style issues in date.[ch]
-Cleanup: make original comments doxygen compatible and remove/change outdated comments

(svn r3181) -Bracing
-Indentation
-Whitespace
-DeMorgan's Law
-Test with NULL or 0 for non-booleans
-'\0' instead of 0 for chars
-Remove redundantly redundant comments (like DoFoo(); // Do foo)
-Join multiple short lines with a single statement
-Split single lines with multiple statements
-Avoid assignments in if

(svn r1407) -Codechange: changed a lot around _stations, _vehicles, _towns and _industries
(in prepare of dynamic arrays):
- DEREF_XXX is changed into GetXXX
- All direct call are directed via GetXXX
- struct Industry has now an index-field
- ENUM'd some stuff
- Replaced home built loops with FOR_ALL_XXX
- Added _stations_size, _vehicles_size, ... which gives the length of the
array (which will be dynamic in the near future)
- Changed lengtof(XXX) to _XXX_size (e.g. _stations_size)
- Removed all endof(XXX) (because mostly it was part of a FOR_ALL_XXX)
- Made the sort-functions of all 4 dynamic
- Made all 4 Initialize functions more of the same
- Some minor tab-fixing and stuff
(tnx to Tron for proof-reading my 100kb patch ;))

Note for all: please do NOT directly call _stations, _vehicles, _towns and
_industries, but use the right wrapper to access them. Thank you.
Ps: please also do not use 'v++', where v is of type Vehicle *.

(svn r1348) -Feature: resizable windows. Read the comment in window.h to find out
how the system works. All useful windows are already made resizable. Enjoy :)
-Fix: fixed some GUI-glitches and flaws along the way

(svn r901) Small step in the process to clean up the DPARAM mess:
- reduce to 2 sizes (*DParam64 for 64bit values, *DParam for the rest)
- use inline functions instead of macros
- add assert()s to check for buffer overruns

(svn r815) Include strings.h only in the files which need it.
This should reduce the compile time after altering english.txt by about 1/3, because "only" 62 instead of 90 .c files must be recompiled.

(svn r177) -Fix: padded out Widget code to solve warnings on C99 compiler (Tron)
-Fix: added WIDGETS_END macro for WWT_LAST which does this for all last widget-types