Format README.md with subsections

Having actual section headers instead of just bold text makes those parts of the document individually linkable.

README.md

 
 
 Features:
+=========
 
 *   Interrupt based movement with real linear acceleration
 *   High steprate
 Differences and additions to the already good Sprinter firmware:
 ================================================================
 
-*Look-ahead:*
+Look-ahead:
+-----------
 
 Marlin has look-ahead. While sprinter has to break and re-accelerate at each corner,
 lookahead will only decelerate and accelerate to a velocity,
 This is only possible, if some future moves are already processed, hence the name.
 It leads to less over-deposition at corners, especially at flat angles.
 
-*Arc support:*
+Arc support:
+------------
 
 Slic3r can find curves that, although broken into segments, were ment to describe an arc.
 Marlin is able to print those arcs. The advantage is the firmware can choose the resolution,
 and can perform the arc with nearly constant velocity, resulting in a nice finish.
 Also, less serial communication is needed.
 
-*Temperature Oversampling:*
+Temperature Oversampling:
+-------------------------
 
 To reduce noise and make the PID-differential term more useful, 16 ADC conversion results are averaged.
 
-*AutoTemp:*
+AutoTemp:
+---------
 
 If your gcode contains a wide spread of extruder velocities, or you realtime change the building speed, the temperature should be changed accordingly.
 Usually, higher speed requires higher temperature.
 If the target temperature is set manually or by gcode to a value less then tempmin, it will be kept without change.
 Ideally, your gcode can be completely free of temperature controls, apart from a M109 S T F in the start.gcode, and a M109 S0 in the end.gcode.
 
-*EEPROM:*
+EEPROM:
+-------
 
 If you know your PID values, the acceleration and max-velocities of your unique machine, you can set them, and finally store them in the EEPROM.
 After each reboot, it will magically load them from EEPROM, independent what your Configuration.h says.
 
-*LCD Menu:*
+LCD Menu:
+---------
 
 If your hardware supports it, you can build yourself a LCD-CardReader+Click+encoder combination. It will enable you to realtime tune temperatures,
 accelerations, velocities, flow rates, select and print files from the SD card, preheat, disable the steppers, and do other fancy stuff.
 One working hardware is documented here: http://www.thingiverse.com/thing:12663
 Also, with just a 20x4 or 16x2 display, useful data is shown.
 
-*SD card folders:*
+SD card folders:
+----------------
 
 If you have an SD card reader attached to your controller, also folders work now. Listing the files in pronterface will show "/path/subpath/file.g".
 You can write to file in a subfolder by specifying a similar text using small letters in the path.
 Also, backup copies of various operating systems are hidden, as well as files not ending with ".g".
 
-*SD card folders:*
+SD card folders:
+----------------
 
 If you place a file auto[0-9].g into the root of the sd card, it will be automatically executed if you boot the printer. The same file will be executed by selecting "Autostart" from the menu.
 First *0 will be performed, than *1 and so on. That way, you can heat up or even print automatically without user interaction.
 
-*Endstop trigger reporting:*
+Endstop trigger reporting:
+--------------------------
 
 If an endstop is hit while moving towards the endstop, the location at which the firmware thinks that the endstop was triggered is outputed on the serial port.
 This is useful, because the user gets a warning message.
 However, also tools like QTMarlin can use this for finding acceptable combinations of velocity+acceleration.
 
-*Coding paradigm:*
+Coding paradigm:
+----------------
 
 Not relevant from a user side, but Marlin was split into thematic junks, and has tried to partially enforced private variables.
 This is intended to make it clearer, what interacts which what, and leads to a higher level of modularization.
 some transfer is information (usually beginning with "echo:"), an error "error:", or just normal protocol,
 necessary for backwards compatibility.
 
-*Interrupt based temperature measurements:*
+Interrupt based temperature measurements:
+-----------------------------------------
 
 An interrupt is used to manage ADC conversions, and enforce checking for critical temperatures.
 This leads to less blocking in the heater management routine.
 The second tells what axis this servo will be attached to. In the example above, we have a servo in Z axis.
 The third one tells the angle in 2 situations: Probing (165º) and resting (60º). Check this with command M280 P0 S{angle} (example: M280 P0 S60 moves the servo to 60º)
 
-*For RAMPS users:*
+For RAMPS users:
+----------------
+
 By default, RAMPS have no power on servo bus (if you happen to have a multimeter, check the voltage on servo power pins).
 In order to get the servo working, you need to supply 5V to 5V pin.. You can do it using your power supply (if it has a 5V output) or jumping the "Vcc" from Arduino to the 5V RAMPS rail.
 These 2 pins are located just between the Reset Button and the yellow fuses... There are marks in the board showing 5V and VCC.. just connect them..