Reorganizing the directory structure

- src/backend/*.* moved to src/api/c/*.*
- src/frontend/cpp renamed as src/api/cpp
Unified the way complex numbers are printed
Merge pull request #162 from pavanky/reorg

Reorganizing source code file hierarchy.
Added linear interpolation for transform (adds for rotate, scale, skew etc)

* TODO add tests
* TODO check if scale can provide same functionality as resize
Merge pull request #163 from shehzan10/transform_linear

Added linear interpolation for transform

- Adds support for rotate, scale, skew
Added tests for bilinear transforms (rotate)
Merge pull request #165 from shehzan10/devel

Added tests for bilinear transforms (rotate)
Fixes for rotate bilinear tests

* Requires higher tolerance for floating point errors
* Enable previously disabled test
Merge branch 'devel' of https://github.com/arrayfire/arrayfire into devel