Add a CMake build

Tried to stay as close as possible to ja2_2019.sln

On Visual Studio 2022 just Project -> CMake Settings for Ja2, add
the x86 configurations you want and press F7.

Below shows how the -DLanguages -DApplications switches work, If you don't
set them, the CMakeCache.txt of them will be set to ENGLISH and JA2,
respectively:

cmake [...] // nothing set, configure just JA2_ENGLISH.exe by default
cmake [...] -DApplications="JA2UB" // configures just Unfinished Business
cmake [...] build -DApplications="JA2UB;JA2UBMAPEDITOR" // Unfinished Business and UB Map Editor
cmake [...] build -DApplications="JA2UB;JA2MAPEDITOR;ALL" // ALL is in the list, configures every application
cmake [...] build -DApplications="JA2MAPEDITOR;DeathStranding" // fatal error: DeathStranding not an application

cmake [...] -DLanguages="GERMAN" // configures just German targets
cmake [...] build -DLanguages="GERMAN;ENGLISH" // German and English
cmake [...] build -DLanguages="GERMAN;ENGLISH;ALL" // ALL is in the list, configures every language
cmake [...] build -DLanguages="ENGLISH;ESPERANTO" // fatal error: ESPERANTO not supported

ext/libpng/CMakeLists.txt

@@ -0,0 +1,20 @@
+add_library(libpng
+"png.c"
+"pngerror.c"
+"pnggccrd.c"
+"pngget.c"
+"pngmem.c"
+"pngpread.c"
+"pngread.c"
+"pngrio.c"
+"pngrtran.c"
+"pngrutil.c"
+"pngset.c"
+"pngtrans.c"
+"pngwio.c"
+"pngwrite.c"
+"pngwtran.c"
+"pngwutil.c"
+)
+target_include_directories(libpng PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_link_libraries(libpng PUBLIC zlib)

ext/zlib/CMakeLists.txt

@@ -0,0 +1,18 @@
+add_library(zlib
+"gzread.c"
+"gzlib.c"
+"gzclose.c"
+"crc32.c"
+"zutil.c"
+"uncompr.c"
+"compress.c"
+"inffast.c"
+"inflate.c"
+"adler32.c"
+"infback.c"
+"deflate.c"
+"gzwrite.c"
+"inftrees.c"
+"trees.c"
+)
+target_include_directories(zlib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})