Add script to build DCMTK with emscripten support

Building dcmdump.js, dcmxml.js, ... can easily be done using a command
similar to this one:

  cmake -DEMSCRIPTEN_ROOT_PATH:PATH=/path/to/emscripten ../dcmjs

EMSCRIPTEN_ROOT_PATH is the directory containing "emcc", "emc++", ...

It is assumed that the Emsscripten.cmake toolchain file will be located in
${EMSCRIPTEN_ROOT_PATH}/cmake/Platform
Update DCMTK project to include automatic gzip'ing of js files.

$ git shortlog a8507c04..6297448
Jean-Christophe Fillion-Robin (1):
      Add post build target to automatically gzip generated .js
Disable automatic loading of executable and keep the runtime env active.

From the documentation [1]:

noInitialRun: If set to true, main() will not be called. The program will
still call global initializers, set up memory initialization, and so forth.
You can then call main() yourself later.

noExitRuntime: If set to true, the runtime is not shut down after run is
called. Shutting down the runtime calls shutdown callbacks, for example
atexit calls. If you want to be able to continue to use the code after
run finishes, it is safer to set this.

$ git shortlog 629744894..7ef3b940
Jean-Christophe Fillion-Robin (2):
      Force gzip'ing of js file even if it already exists.
      Associate a "pre" javascript file to customize generated js files.

[1] https://github.com/kripken/emscripten/wiki/Interacting-with-code
Add build instruction for cross compiling using CMake
Merge branch 'superbuild-dcmtk-with-emscripten-support'

* superbuild-dcmtk-with-emscripten-support:
  Add build instruction for cross compiling using CMake
  Disable automatic loading of executable and keep the runtime env active.
  Update DCMTK project to include automatic gzip'ing of js files.
  Add script to build DCMTK with emscripten support
Add commas to json object definition (runtime syntax error)
Support large dicom files

allow emscripten to grow memory as needed (compile-time option).

Does generate warnings, which we may want to suppress later.
Enable PNG support in DCMTK

Also generalize who Emscripten compiler and flags are passed to the
different projects.
Do not associated any langage with top-level project
Merge branch 'add-png-support'

* add-png-support:
  Do not associated any langage with top-level project
  Enable PNG support in DCMTK
Add dcmjs.js - wrapper around a configured set of dcmtk applications

Instead of generating on .js file for each application, a single dcmjs.js
script is now generated. It is basically a wrapper allowing to
execute any dcmtk application.
Merge branch 'generate-dcmjs-wrapper'

* generate-dcmjs-wrapper:
  Add dcmjs.js - wrapper around a configured set of dcmtk applications
Do not use recently added gzip option -k. Fixes #6

Since the gzip option "-k" has been added fairly recently [1], this commit
implement a workaround that (1) backup the script, (2) gzip it in place
and (3) copy the backup to its original name.

[1] http://lists.gnu.org/archive/html/bug-gzip/2013-04/msg00010.html
Enable "xml2dcm" application

This commit add LibXml2 library so that the "xml2dcm" application
is built with xml support.
Shut up missing openlog/closelog/syslog symbols warnings. Fixes #1