frame-benchmarking support

[clangenb]

I have noticed that the runtime didn't really like when the benchmarking macro from this repository is mixed with the benchmarking macro from substrate. Hence, I have re-implemented the orml-vesting benchmarks with substrate's macro, here.

It only contains the benchmarks for the orml-vesting pallet currently. Is this something that you'd be interested in having upstreamed?

[xlc]

yeah that will be great. the new benchmark syntax and omni bencher have solved a lot of issues that the old one had and now it is a good time to migrate to it