Non-conflicting names

Using this library in a file along with iostream caused a compilation
error. The “#define min” line in RF24_config.h overrode a function by
the same name used in a file included by iostream. Renamed to avoid
this issue.
Merge pull request #38 from jfktrey/master

Non-conflicting names
Fix for last pull request

- Goes to show that even the simplest of changes should be tested...
#43
Merge remote-tracking branch 'upstream/master'