DORIS RINEX processing

[gwbres]

@ChristopherRabotin,

A new doris branch attempts at answering Discussion #77

The fundemental issue is how to correctly describe the DORIS measurements in time.
They are published in the DORIS timescale, with means to relate the observations to TAI.
My plan, since we cannot represent "DORIS", is to find means to store them as TAI by applying the correct offset.
Not sure this is entirely feasible at the moment.

[gwbres]

@ChristopherRabotin,

making good progress, parsing is almost complete. Now I will have to spend a few days verify the observation mode correctly applies to these files, and see if we can propose a couple of interesting operations dedicated to this new format

[gwbres]

Partial support initiated, files are parsed somewhat sucessfully.
Next PR will verify this parsing thoroughly and at least unlock the -g option in the CLI toolbox