Various typo fixes - only in comments, no code changes.

Marlin/Servo.h

 
   Note that analogWrite of PWM on pins associated with the timer are disabled when the first servo is attached.
   Timers are seized as needed in groups of 12 servos - 24 servos use two timers, 48 servos will use four.
-  The sequence used to sieze timers is defined in timers.h
+  The sequence used to seize timers is defined in timers.h
 
   The methods are:
 
 /*
  * Defines for 16 bit timers used with  Servo library
  *
- * If _useTimerX is defined then TimerX is a 16 bit timer on the curent board
+ * If _useTimerX is defined then TimerX is a 16 bit timer on the current board
  * timer16_Sequence_t enumerates the sequence that the timers should be allocated
  * _Nbr_16timers indicates how many 16 bit timers are available.
  *
 typedef enum { _Nbr_16timers } timer16_Sequence_t ;
 #endif
 
-#define Servo_VERSION           2      // software version of this library
+#define Servo_VERSION           2     // software version of this library
 
 #define MIN_PULSE_WIDTH       544     // the shortest pulse sent to a servo
 #define MAX_PULSE_WIDTH      2400     // the longest pulse sent to a servo
 #define DEFAULT_PULSE_WIDTH  1500     // default pulse width when servo is attached
-#define REFRESH_INTERVAL    20000     // minumim time to refresh servos in microseconds
+#define REFRESH_INTERVAL    20000     // minimum time to refresh servos in microseconds
 
 #define SERVOS_PER_TIMER       12     // the maximum number of servos controlled by one timer
 #define MAX_SERVOS   (_Nbr_16timers  * SERVOS_PER_TIMER)
   uint8_t attach(int pin);           // attach the given pin to the next free channel, sets pinMode, returns channel number or 0 if failure
   uint8_t attach(int pin, int min, int max); // as above but also sets min and max values for writes.
   void detach();
-  void write(int value);             // if value is < 200 its treated as an angle, otherwise as pulse width in microseconds
+  void write(int value);             // if value is < 200 it is treated as an angle, otherwise as pulse width in microseconds
   void writeMicroseconds(int value); // Write pulse width in microseconds
   int read();                        // returns current pulse width as an angle between 0 and 180 degrees
   int readMicroseconds();            // returns current pulse width in microseconds for this servo (was read_us() in first release)
   bool attached();                   // return true if this servo is attached, otherwise false
 #if defined (ENABLE_AUTO_BED_LEVELING) && (PROBE_SERVO_DEACTIVATION_DELAY > 0)
-  int pin;                           // store the hw pin of the servo
+  int pin;                           // store the hardware pin of the servo
 #endif
 private:
    uint8_t servoIndex;               // index into the channel data for this servo

Marlin/fastio.h

 /*
-  This code contibuted by Triffid_Hunter and modified by Kliment
+  This code contributed by Triffid_Hunter and modified by Kliment
   why double up on these macros? see http://gcc.gnu.org/onlinedocs/cpp/Stringification.html
 */
 

Marlin/stepper.h

 void st_wake_up();
 
   
-void checkHitEndstops(); //call from somwhere to create an serial error message with the locations the endstops where hit, in case they were triggered
-void endstops_hit_on_purpose(); //avoid creation of the message, i.e. after homeing and before a routine call of checkHitEndstops();
+void checkHitEndstops(); //call from somewhere to create an serial error message with the locations the endstops where hit, in case they were triggered
+void endstops_hit_on_purpose(); //avoid creation of the message, i.e. after homing and before a routine call of checkHitEndstops();
 
 void enable_endstops(bool check); // Enable/disable endstop checking
 

Marlin/temperature.h

 #endif
 
 // public functions
-void tp_init();  //initialise the heating
+void tp_init();  //initialize the heating
 void manage_heater(); //it is critical that this is called periodically.
 
 // low level conversion routines