Separate lwip configuration files from code

[christian-herber]

For integration purposes and flexibility, it is important to separate application code from configuration files (e.g. to include configuration files from a location outside of this git)

currently, the following config files are in the git:

• include/coap2/lwippools.h (this is quite odd. other applications might also need to define memory pools, so this shouldn't be in the main include directory)
• examples/lwip/lwipopts.h (same directory contains the header for server examples)

Propsed Solution:

Move both files into a separate folder examples/lwip/config
While we are at it, also move coap_config.h (respectively the link to it)

This will create a single folder containing the configuration files.

[mrdeep1]

libcoap LwIP support has been re-written in PR #884, and so this should no longer be an issue. Configuration files are now in the examples/lwip.config/ directory.

[mrdeep1]

Closed as fixed in #926 which is now in the develop branch. There is now a config directory.