Unified CMake-based build system

See #56 for discussion.

Fixes #21, Fixes #29, Fixes #37, Closes #56, Fixes #58, Closes #73
Obviates #82

See also:
https://sourceforge.net/p/libjpeg-turbo/feature-requests/5/
https://sourceforge.net/p/libjpeg-turbo/patches/5/

appveyor.yml

@@ -16,11 +16,11 @@ install:
 
       set MSYSTEM=MINGW32
 
-      bash -c "pacman --noconfirm -S autoconf automake libtool zip"
+      bash -c "pacman --noconfirm -S zip"
 
       mklink /d "%ProgramData%\Oracle\Java32" "c:\Program Files (x86)\Java\jdk1.6.0"
 
-      git clone --depth=1 https://github.com/libjpeg-turbo/buildscripts.git c:/buildscripts
+      git clone --depth=1 https://github.com/libjpeg-turbo/buildscripts.git -b %APPVEYOR_REPO_BRANCH% c:/buildscripts
 
 build_script:
   - cmd: >-