Consider separating the concept of pin modes and configuration

[soundanalogous]

Currently pin modes contain a mix of actual pin modes (digital in, digital out, pwm, etc) and configuration (Servo, OneWire, Encoder, etc). A better approach would be to separate these concepts. Pin modes should be the actual HW modes supported by each pin on a board. For example:

OUTPUT
INPUT
ANALOG
PWM

Instead of "I2C" the modes should be:
SDA
SCL

Instead of "SPI" (if ever added to Firmata) the modes should be:
MISO
MOSI
SCK
SS

If UART support is added the modes should be:
UART_RX0
UART_TX0
If multiple UARTs
UART_RX1
UART_TX1
etc...

This concept should be distinct from hardware abstractions associated with specific pins:

Servo
Shift
OneWire (unless such a thing as HW OneWire exists on a particular board)
Encoder
Stepper