Handling common binary ZK file formats

Parsing (and later maybe also writing) commonly used binary ZK file formats:

• .ptau files used by snarkjs, phase2-bn254 and others to encode the results of the "powers of tau" trusted ceremony
• .r1cs files, describing R1CS circuits used by circom, snarkjs and others
• .wtns files, used by circom and snarkjs to encode the witness
• .sym files used by circom and snarks to describe mapping of names to witness indices

Note: the JSON-based formats are in a separate library, to avoid the unnecessary aeson dependency hell.

iden3 binary containers

The formats .r1cs, .wtns and .ptau share a common generic structure. This format is very simple: There is a global header, and then several sections. The actual content of the sections is format-dependent.

The .r1cs format is specified here: https://github.com/iden3/r1csfile/blob/master/doc/r1cs_bin_format.md