The term "backend" can be confusing because it can refer to both the
virtual function table and the device/parser backends. The use of the
term "vtable" avoids this.
The d9 backend already reads the version info, to autodetect the
protocol variant. When doing the same in the vyper2 backend, we don't
have to read the version info again when downloading the dives.
I forgot to update the device and parser initialization functions to
store the context pointer into the objects. As a result, the internal
context pointers were always NULL.
Adding the "dc_" namespace prefix (which is of course an abbreviation
for libdivecomputer) should avoid conflicts with other libraries. For
the time being, only the high-level device and parser layers are
changed.
The D9tx, D6i and D4i have twice the amount of memory compared to the
previous versions (64K versus 32K). To support both variants, a new
layout descriptor is introduced.
Using a resizable memory buffer allows to allocate the right amount of
memory inside the backend, avoiding having to know the required buffer
size in advance.
