Fix Markdown in README.md

GitHub's Markdown interpreter was recently changed to strictly enforce
the GFM spec. This has caused some Markdown to no longer display as
originally intended. The anchor links I added were actually unnecessary
because the Markdown automatically generates these for every header.

README.md

@@ -7,7 +7,6 @@ AVR microcontrollers provide hardware PWM on some pins but if you need PWM on ot
 
 This library is licensed under [BSD3](https://opensource.org/licenses/BSD-3-Clause)
 
-<a id="installation"/>
 #### Installation
 - Download the most recent version here: https://github.com/Palatis/arduino-softpwm/archive/master.zip
 - Using Arduino IDE 1.0.x:
@@ -16,7 +15,6 @@ This library is licensed under [BSD3](https://opensource.org/licenses/BSD-3-Clau
   - Sketch > Include Library > Add ZIP Library... > select the downloaded file > Open
 
 
-<a id="usage"/>
 #### Usage
 See **File > Examples > arduino-softpwm > SoftPWM_example** for demonstration of library usage.
 
@@ -68,7 +66,6 @@ Alternatively, you can add `using namespace Palatis;` at the top of the source f
 `SoftPWM.allOff()` - Set the PWM value of all channels to 0.
 
 
-<a id="troubleshooting"/>
 #### Troubleshooting
 - LEDs have a visible flicker, especially noticeable when the LED is moving relative to the viewer.
   - The PWM frequency set in `SoftPWM.begin()` is too low. Use `SoftPWM.printInterruptLoad()` to determine the optimum PWM frequency. You may be able to achieve a higher PWM frequency by setting less PWM levels with `SOFTPWM_DEFINE_OBJECT_WITH_PWM_LEVELS()` or `SOFTPWM_DEFINE_EXTERN_OBJECT_WITH_PWM_LEVELS()`.