Adds support for new "Rotate" log mode (issue #244)

* Removed extra comments related to MAX_CFG (could be confusing to future developers)
* Added two new parameters to config file (Max Filesize and Max Filenumber, both only used in MODE_ROTATE)
* Added new mode (3) : MODE_ROTATE
* Added debug prints to help see max filesize and max filenumber (inside #if DEBUG)
* Commented out decrimenting newFileNumber when it is read from EEPROM
* Added three new entries to the 'set' menu:
*  4) - Sets mode to MODE_ROTATE
*  8) and 9) - sets the new Max Filesize and Max Filenumber config values
* Added code to print out max fileszie and file number at top of 'set' menu
* Updated 'set' menu strings to be more descriptive
* Fixed 'set' menu 7) (set number of escape characters) with new routine getSerialByte() to read in a 3 digit integer properly rather than a single character
* Added code to save/ restore Max Filesize and Max Filenumber from EEPROM and config file

NOTE: Crashes happen when returning from "set" menu after certain operations if compiled with latest Arduino IDE. Tested with 1.6.8 and it works fine. (See issue #245 for more details)

Author: EmbeddedMan