Ultimate followup to Stepper/Planner patch

- Search all symbols and apply prefixes where needed
- Encapsulate some private methods
- Inline some setters
- Make `microstep_mode` a public method

Marlin/planner.cpp

@@ -21,25 +21,13 @@
  */
 
 /**
- * planner.cpp - Buffer movement commands and manage the acceleration profile plan
- * Part of Grbl
+ * planner.cpp
  *
+ * Buffer movement commands and manage the acceleration profile plan
+ *
+ * Derived from Grbl
  * Copyright (c) 2009-2011 Simen Svale Skogsrud
  *
- * Grbl is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Grbl is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Grbl.  If not, see <http://www.gnu.org/licenses/>.
- *
- *
  * The ring buffer implementation gleaned from the wiring_serial library by David A. Mellis.
  *
  *