add AMD scratchpad indexing option

fix Releases link

Change the default for strided index. Th euser feedback shows that strided_index = true will give a view hashes more per second.

Allow to change the indexing used to address the hash scratchpad memory.

- add option `strided_index` for each gpu

add environment variable `XMRSTAK_NOWIT`

- add documentation
- add environment variable `XMRSTAK_NOWAIT`

experimental warning: portable binaries

Really fixing incorrect Releases URL in README.md#Download

add warning that portable binaries are experimental

:)

Add custom message for dev -> user pool switch

Add custom message for dev -> user pool switch

update windows build documentation

fix CMake 

add hint that the new compiled xmr-stak-dep must be used for the new VS tool chain

- remove all `"${VARNAME}` usages in if conditions
- increase cmake minimum version to 3.1 to have the new behavior of [CMP0054](https://cmake.org/cmake/help/v3.1/policy/CMP0054.html)

- fix wrong compare for HWLOC not found
- remove usage of microhttpd variable if microhttpd is disabled

Adding Dockerfile and fixing build_xmr-stak_docker script

Fixed incorrect Releases URL in README.md#Download

fix CUDA launch bounds usage

fix auto suggestion for low end devices 

fix #191

lauch bounds must be placed before the return type but after the template paramater

Add compilation instructions for MacOS

Fix for AMD GPU detection on MacOS X

update windows compile guide  

add missing nvidia help to usage.md

add NVIDIA cli options to the help message

Update gpu.hpp

Fix indent on hash rate report.

Fix for AMD GPU detection on MacOS X
On MacOS X the platform is reported as Apple, and the vendor is reported as AMD.

Fix crash on FreeBSD (#177)

Fixing the compile error on MacOS X

Fix uninitialized memory accces

fix appvoyer

Uninitialized memory access is UB in C/C++, fix it.