Added BBB-analog-in

Added a triggered analogue input node
Added BBB-digital-in

Added digital input node - initially this is just BBB-discrete-in
Attempting to get the initial message

Modified 145-digital-in.js adding various debugs to try and trace why
the initial messages don’t appear
Added activeLow property to discrete-in

Further attempts to get the initial message working. Added activeLow
property. Output messages now include topic. Better help text. Change
name to discrete-in
Debugging discrete-in

Coerce the currentState to always be numeric & use === tests
Catch the first spurious interrupt when x.value is undefined
Add more debug output
Add a second timer to get the first message out. This still fails at
node-RED startup when the node is not activeLow
Debug & tidy up

Make the colours the same as the RPi equivalents. Remove ‘BBB’ from the
node names.
Further debug output
Polishing discrete-in a bit

Commented out debug: added numeric validator
Starting to add scale factors & linearisation

Added breakpoints property to the node
Building the breakpoints editor (nearly there!)
Finshing off the breakpoint editor

Mutable/immutable behaviour of breakpoints completed, and the 0 and 1
input values are no longer editable.
Adding a breakpoint now inserts it in the list in next-to-last
place, with sensible default values.
Added analogue scaling & averaging; discrete check reads

Added input scaling function and averaging of multiple readings for
noise reduction to the analogue input node.
Added the ‘sanity check’ read of the digital input pin to the timer
callback in the discrete input node
Added pulse-in; added debouncing

Added the pulse-in node code. Added simple debouncing logic to
discrete-in (note: this implementation may be badly affected if there
is a lot of very fast bouncing.
Merge branch 'master' into beaglebone-black-hardware
Fixed issues with pulse-in; minor bug fixes

Got the pulse-in node working properly, and tidied up a few E&O in the
other nodes
Added discrete-out node

The output node is currently in 145-digital-in. This situation is
hopefully only temporary…
Added message output to discrete-out
Added pulse-out node
Changed comments to match the format used in 145-digital-in.*
Moved all nodes into one common .js file & .html file pair
Correct file name in error message
Tidy up & add README.md

Converted tabs to spaces as required