instructions for new gcc versions

Yet another nicehash workaround -.-

Add filename to backend errors

New thumbnail

POW AEON v7

- documentation: change `aeon` to `aeon7`
- change `case` order in `switch` statements
- update README.txt

add cli option `--noAMDCache`

allow to disable the OpenCl cache
  - usefull for read only systems
  - usefull for unknown errors during cache reading

fix parentheses warning

documentation: name a worker

fix autoAdjust(non hwloc)

fix warning

```
/Users/user/xmr-stak/xmrstak/backend/amd/amd_gpu/gpu.cpp:481:11: warning: using the result of an assignment as a condition without parentheses [-Wparentheses]
                if( ret = clGetProgramInfo(ctx->Program, CL_PROGRAM_BINARIES, num_devices * sizeof(char*), all_programs.data(),NULL) != CL_SUCCESS)
```

add note that `rig_id` is ignored by some pools

- add new pow for AEON
- fix missing cryptonight-heavy selection for multi hashes

- add tests whith disabled dependencies

- remove call `IsCurrencyMonero` with `cn_select_memory`

reenable MACOSX travis tests

remove old release signatures

the signatures for the next release will be in the release note itself

Change video guide to a placeholder link

rename `monero2` to `monero7`

fixAMD benchmark mode

revert input size change

fix #1202

move option currency down

revert #1198, the block size is limited to 84byte

move option `--currency` down

OpenCL precompiled code message

increase version to 2.3.0

The OpenCl code is only supporting jobs up to 84byte

change warning when precompiled OpenCL code is not found

Fix input buffer size cuda