Reverted changes to .gitignore, we are using CMake
Refactored the code strcuture for unit testing.

Changes:
1. Moved privete (unpublished) headers into sub-folder
   'include/ninety47/dukascopy'
2. Moved anonymous namespace from 'src/dukascopy.cpp' into
   'inlcude/ninety47/dukascopy/lzma.h' and 'src/lzma.cpp'
3. Update CMakeList.txt to add new src file.
4. Introcued N47_E_OK def now that LZMA and ELZMA is hidden
   from 'src/duakscopy.cpp'.

Fixes:
1. 'include/ninety47/defs.h' didn't have circular include
   protection.

Refs: #3