fix bug announced in #52

If the miner is compiled in debug mode the assert condition results in a compile time error.

Early returns within a kernel can have unexpected behavior, this strongly depends on the opencl
runtime compiler. To avoid errors all early returns are removed.
There is no negative effect(e.g.performance) if the threads stay alive up to the end of the kernel.

One source for the early return is: http://al-key-opencl.blogspot.de/2014/09/be-careful-not-to-mix-early-return-and.html

This pull request also fix a race condition where all fill the shared memory.
Also a bug introduced with #16 is fixed, because of the early return not was possible that
the last block works with an wrong initilized shared memory (result should be a wrong hash if the result target size is valid).

Is is possible that the number of results are greater than the result output array,
in this case invalid memory can be access within the device and on the host side.

check that the number of global threads is a multiple of the workgroup size

The number of threads within a kernel must be a multiple of the worksize.
If not it can crash on some systems.

- string literal can only be 16kbyte

- move source code to `src`
- categorize files and move to group folder
- change upper case class files to lower case
- change C++ header to `*.hpp`