Avoid naming conflict of header files.

[erlingrj]

Some of the header files have very common names like "platform.h" and "port.h". This is already causing problems when porting it to XMOS. Likely this will cause problems when integrating reactor-c with other libraries and projects. There seems to be two ways to solve this.

1. Renaming:
   platform -> lf_platform, port -> lf_port etc.

2. Use paths (thanks Christian :))
   We can move all the header files out of the "core" folder and into the "include" folder. We put them like this:

core
include
-- reactor-c
---- platform.h
---- port.h
---- platform
------ lf_arduino.h

Then we put ~/include on the include path. This means that you have to do #include "reactor-c/platform.h" for all includes. I.e. you have to prepend reactor-c to all your includes. I think this latter solution is cleanest. We can at the same remove the symlink from include/core to core.

[lhstrh]

Based on conversation on Zulip, it appears that everyone so far is in favor of option 2.

[erlingrj]

OK. I will make a PR for this soon.

[gundralaa]

#147
Changed for lf_types for nrf port