* add support for dram data retention (#414)

* Added new github examples for ddr data retention (#426)

* Added new github examples for ddr data retention

* fixing link to runtime software test

* removing temporary & executable file from github

* new error codes for data retention (#445)

* Enable data retention. (#447)

* upgrading data retention branch to devkit  1.4.2

* porting backdoor DDR load & AXI_MEMORY_MODEL simulation features to data retention customer TB for future simulation support.

* updating default AFI to a data retention enabled 4-ddr calibration AFI

* updating dataretention branch to develop

* [2017.4 Data Retention] Backward compatibility (#454)

* Load without data retention if load failed

If failed for reasons FPGA_ERR_DRAM_DATA_RETENTION_NOT_POSSIBLE, FPGA_ERR_DRAM_DATA_RETENTION_FAILED, or FPGA_ERR_DRAM_DATA_RETENTION_SETUP_FAILED.

* Info message

Print an info message when load failed data retention.

* added data retention documentation (#453)

* added data retention documentation

* updated data retention docs

* Linking to data retention documents from top

* refining description of data retention feature

* adding asl license header for 2018

* fixing link for now. will add back after merging PR461

* Allow for spaces in a longer header comment

* Adding apache headers and updated asl 2018 header

* cl_dram_dma example cleanup (#461)

* added data retention documentation

* updated data retention docs

* created fpga_dma library

* customer example clean up for cl_dram_dma, plus data retention example

* cosim

* updated licence headers

* cosim-fix

* documentation updates for data retention (#462)

* doc updates

* doc updates

* doc updates

* doc updates

* doc updates

* adding sdaccel data retention example

* adding license header to Makefile

* fixing makefile switches

* fixing typo in license header