Add support for one memory section duplicated in two memory areas.

[AndersHoglund]

Typically in an embedded application the .data section occupies space in both FLASH and RAM. Currently it seems as only RAM is supported. Please take look at the linker command files attached in PR #37., where the .data spec looks like this :

  .data :
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */

    . = ALIGN(4);
     _edata = .;        /* define a global symbol at data end */
  } >RAM AT> FLASH

The closing line indicates that .data exists in both RAM (run time) and FLASH (initializers)