Remove redundancy in filenames about libsnark

[dtebbs]

There may be a few more moving parts to this kind of change.

It's pretty common to name files to be consistent with the name of the (main) class they contain, and I think this kind of consistency (file name and class name) is significantly more important than removing a little redundancy in file names. Indeed, some languages actually enforce this kind of rule on class and file names.

We can remove the redundancy in the file names, but in that case I think we need to make better use of namespaces so that the file gadgetlib1/pairing/mnt/pairing_params.hpp contains the class libsnark::gadgetlib1::pairing::mnt::pairing_params, and not a class called mnt_pairing_params.

Also related to #29 (comment)

[AntoineRondelet]

Yes this is a good point you're making here @dtebbs
I would be keen to think more about using namespaces in the various code bases. There is room for better code organization and separation here as we mostly use a single "holdall" namespace so far. I mean, the main namespaces are lib<name> and test as far as I remember. We use an internal namespace at one point in Zeth, but we generally do not have a very refined way of exposing the code in our cpp libraries. There may be an argument to change that down the road and use more layers of namespaces.