DMapBuilder Changes

    * New Code for Restructured DMap file
    * Added Tests scenarios for Builder
Additional checks and fixed broken test

    * Added additional check for data length before writing to block
    * Added check for successful temp file creation before writing.
    * Fixed the "exceedingBlockSizeTest"
Improved handling of values during map creation

    * Instead of loading all key-values into memory, values are loaded
      only while writing to map file.

    * Tests added for duplicate key handling and sorted keys in block.
Merge pull request #2 from vvenkatr/DMapBuilder_restructure_file

DMapBuilder new file structure.
Allows the block-wise loading of data.