Rough merge of upstream libdivecomputer.
This is mainly about making the new iostream code upstream, although we
don't actually use it.
It abstracts out the the old serial and usbhid code, but we end up still
using our own 'custom_io' interface because the iostream code doesn't do
it right.
* jef/master:
Correctly determine git SHA if libdivecomputer is a git submodule
Don't accept a NULL pointer as parameter
Add support for semi-closed circuit diving
Detect dives with invalid profile data
Implement the serial communication functions as no-ops
Move the socket code to a common file
Add support for a custom I/O implementation
Port the USB HID code to the new I/O interface
Port the bluetooth code to the new I/O interface
Port the IrDA code to the new I/O interface
Port the serial code to the new I/O interface
Add a new abstract I/O interface
Post release version bump to 0.7.0
8a34d822ff