Set README.md as mainpage of doxygen document.

To allow doxygen link the class name inside README.md with class explanation,
Remove the explicit link to the sub-md files inside README.md

Author: suikan4github

Doxyfile

@@ -943,7 +943,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = src
+INPUT                  = src README.md
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses
@@ -1153,7 +1153,7 @@ FILTER_SOURCE_PATTERNS =
 # (index.html). This can be useful if you have a project on for instance GitHub
 # and want to reuse the introduction page also for the doxygen output.
 
-USE_MDFILE_AS_MAINPAGE =
+USE_MDFILE_AS_MAINPAGE = README.md
 
 # The Fortran standard specifies that for fixed formatted Fortran code all
 # characters from position 72 are to be considered as comment. A common

README.md

@@ -1,20 +1,20 @@
 # Raspberry Pi Pico Driver class collection
-A Collection of the Raspberry Pi [Pico](https://www.raspberrypi.com/products/raspberry-pi-pico/)/[Pico2](https://www.raspberrypi.com/products/raspberry-pi-pico-2/) classes. Also, the [SDK API](https://www.raspberrypi.com/documentation/pico-sdk/hardware.html#group_sm_config_1gaed7a6e7dc4f1979c7c62e4773df8c79b) wrapper class is provided. 
+A Collection of the Raspberry Pi [Pico](https://www.raspberrypi.com/products/raspberry-pi-pico/)/[Pico2](https://www.raspberrypi.com/products/raspberry-pi-pico-2/) classes. Also, a [SDK API](https://www.raspberrypi.com/documentation/pico-sdk/hardware.html#group_sm_config_1gaed7a6e7dc4f1979c7c62e4773df8c79b) wrapper class is provided. 
 
-[HTML documentation](https://suikan4github.github.io/rpp_driver/) is available. 
+An online [HTML documentation](https://suikan4github.github.io/rpp_driver/) is available for the details.  
 
 # Details
 This class collection ( or class library ) encapsule the certain data inside class. And it also allows you to use the dependency-injection inside your project. So, you can test your code with [Google Test](https://github.com/google/googletest) before testing on the target hardware. 
 
 These classes are provided in this version. 
 
-| class                                                  | Description |
-|---------------------------------                       |----------------------------- |
-| ::rpp_driver::[SdkWrapper](docs/sdkwrapper.md)         | Wrapper class of Pico SDK    |
-| ::rpp_driver::[GpioBasic](docs/gpiobasic.md)           | Basic GPIO controller        |
-| ::rpp_driver::[I2cMaster](docs/i2cmaster.md)           | I2C Master controller        |
-| ::rpp_driver::[I2sSlaveDuplex](docs/i2sslaveduplex.md) | Polling based PIO I2S driver |
-| ::rpp_driver::[Adau1361](docs/adau1361.md)             | Audio CODEC driver           |
+| class                             | Description |
+|---------------------------------  |----------------------------- |
+| ::rpp_driver::SdkWrapper          | Wrapper class of Pico SDK    |
+| ::rpp_driver::GpioBasic           | Basic GPIO controller        |
+| ::rpp_driver::I2cMaster           | I2C Master controller        |
+| ::rpp_driver::I2sSlaveDuplex      | Polling based PIO I2S driver |
+| ::rpp_driver::Adau1361            | Audio CODEC driver           |
 
 
 ## How to obtain this project