Documented Auto Bed Leveling

Added a read me file for Auto Bed Leveling for the Solidoodle Printer
Updated ABL Read Me

1. Included line breaks at 80 chars
2. Removed Solidoodle specific references
3. Added a few more parameters — Safe Homing and Accurate Bed Leveling
Merge pull request #6 from MissionSt/missionst/abl-docs

Documented Auto Bed Leveling