First Release Candidate for 0.3.0 release

Add int64 as label type and set it as default (NVIDIA#125)

Fix TF example

Update nvJPEG to 0.1.2 (NVIDIA#79) (NVIDIA#86)

Signed-off-by: Cliff Woolley <[email protected]>

Merge commit for internal changes

 - 02f2c8f - CUDA 9.0 Toolkit is no longer required for pre-built binaries @cliffwoolley
 - 696d5ff - Make only API functions exposed. @JanuszL
 - 26ce6ac - Rework ABI compatibility @cliffwoolley
 - e320b7e - Namespace prefix C API @cliffwoolley
 - 71c7eb7 - logging.warn() is obsolete @cliffwoolley
 - 7bca211 - Fix crash when no files are loaded by reader @JanuszL
 - 9e4cdab - Test importing DALI simultaneously w/ every framework @cliffwoolley

Initial code drop