This PR adds a software SPI implementation. Firstly this removes the
absolute necessity for spidev (#140), which also means when it's not
present things still work (effectively fixes#185), and also enables any
four pins to be used for SPI devices (which don't require the hardware
implementation).
The software implementation is simplistic but still supports clock
polarity and phase, select-high, and variable bits per word. However it
doesn't allow precise speeds to be implemented because it just wibbles
the clock as fast as it can (which being pure Python isn't actually that
fast).
Finally, because this PR involves creating a framework for "shared"
devices (like SPI devices with multiple channels), it made sense to bung
Energenie (#69) in as wells as this is a really simple shared device.
This commit is a fairly major piece of work that abstracts all pin
operations (function, state, edge detection, PWM, etc.) into a base
"Pin" class which is then used by input/output/composite devices to
perform all required configuration.
The idea is to pave the way for I2C based IO extenders which can present
additional GPIO ports with similar capabilities to the Pi's "native"
GPIO ports. As a bonus it also abstracts away the reliance on the
RPi.GPIO library to allow alternative pin implementations (e.g. using
RPIO to take advantage of DMA based PWM), or even pure Python
implementations.
The prototypes in the docs are rigged to make out the first parameter as
mandatory (as it effectively is); however this does mean you've got to
remember to update the prototype when you modify it in the code! :)
Knew I'd missed some patches to the docs! This re-applies the
aforementioned doc patches and also fixes the last RGBLED example (which
was subtly incorrect in the original docs)
Change parent of PWMOutputDevice to OutputDevice and implement blink to
maintain compatibility. The version of blink implemented here is
slightly extended to include functionality like Explorer HAT's "pulse".
The parameter defaults behave identically to OutputDevice's blink but
can be adjusted to have the device smoothly fade in and out.
