Will dpdata support LASP arc-format and MS-car format file?

[QuantumMisaka]

I already have lots of DFT dataset stored by .arc format file. generated by LASP method by using VASP to labeled.
The example of structure file allstr.arc and corresponding force and stress file allfor.arc are below:

arcfile_example.tar.gz

And I desired to transfer it to LabeledSystem format in dpdata. and use it in DeePMD
Also, a single allstr.arc file can be transfer to System format.
which can be easily exported from Materials $tudio , and is also LASP output file.

A simple way is to transfer allstr.arc and allfor.arc data to OUTCAR format. and then use dpdata
but I think the best way is to add support to this arc file in dpdata
If supported, it will be an easy way to use "Surface Stochastic Walking" method by LASP to generate dataset for DeePMD.

I already have the will to do it. However, while I'm familiar in treating allstr.arc and allfor.arc by using single python script, I'm not very familiar with dpdata. So I'd like to have some discussion about the support and it's coding, Thanks!

[njzjz]

I added documentation for the Format class in #451.