Improving ATtinyX61 board definition; verifying fuse and examples.
Correcting Analog pin symbols for TinyX4 and TinyX61.
Fixing PWM pins for Mega.
Revert to saved.
Adding support for DS1302 Trickle-Charge Timekeeping Chip.
Adding some news.
Correcting PWM pin handling for TINYX4 and TINYX5. Verifying all PWM pins.
Improving CC1101 synchronization (wait for SO to go low).
Additional CC1101 command synchronization to improve robustness.
Adding example sketch with 3X4 keypad decoder using an LCD adapter (PCF8574).

1. Fixing input handling on port expander.
2. Updating PCF8574 example sketch.
3. Adding a new example sketch for the PCF8574 device driver. Used to decode
a 3X4 keypad.
Double check number of bytes in receiver FIFO.
Adding check of port read.
Adding SD card low-level SPI device driver.
Adding implementation of SPI::set_clock() to allow dynamic change of clock.
Adding support for SD CID/CSD information (card information).
Updating static DS18B20::convert_request() to omit conversion wait.
Improving documentation of circuit and wiring.
Restructuring SD. Adding the SPI/Driver directory.
Adding support for FAT16/SD. Creating structure for File Systems (FS).
Adding some news.