Change "RC6" to "RCBugFix" on top part of the readme, etc

・Change "RC6" to "RCBugFix" on top part of the readme
・Unify distribution date of RCBugFix and RC6
・Move comments about IDE version from RCBugFix section to RC6 section

README.md

 <img align="top" width=175 src="Documentation/Logo/Marlin%20Logo%20GitHub.png" />
  Additional documentation can be found in [The Marlin Wiki](https://github.com/MarlinFirmware/Marlin/wiki).
 
-## Release Candidate -- Marlin 1.1.0-RC6 - 24 April 2016
+## Release Candidate -- Marlin 1.1.0-RCBugFix - 27 April 2016
 
 __Not for production use – use with caution!__
 
 
 ## Recent Changes
 - RCBugFix
-  - Throw error if compiling with older versions (<1.60) of Arduino due to serious problems with outdated Arduino versions
-  - Please upgrade your IDE at least to Arduino 1.6.0. Thanks.
 
-- RC6 - 23 Apr 2016
+- RC6 - 24 Apr 2016
   - Completed support for CoreXY / CoreXZ in planner
   - Changes to positioning behavior
   - Various issues fixed. More details pending.
+  - Throw error if compiling with older versions (<1.60) of Arduino due to serious problems with outdated Arduino versions
+  - Please upgrade your IDE at least to Arduino 1.6.0. Thanks.
 
 - RC5 - 01 Apr 2016
   - Warn if compiling with older versions (<1.50) of Arduino