Create benchmarks for base64

[fabianfett]

Motivation

We love benchmarks. In order to ensure that our base64 performance does not regress we should have a bunch of benchmarks that test different aspects. Since we will have a bunch of those in the future lets get them into a separate target.

Changes

• Create Base64Benchmarks target
• Add Base64 benchmarks
  • Use scaling factor one if the example data is sufficiently large (1MB)
  • Use scaling factor kilo if the example data is so small that measuring perfs overhead is to large (mostly in the jwt head examples)

Result

We have baselines to test against.

[kperryua]

@swift-ci test

[parkera]

@swift-ci test

[parkera]

Oops - @kperryua already did that 😛

[parkera]

Looks good to me. Will merge soon after I make sure we don't conflict with other benchmark work.

[parkera]

Thanks so much @fabianfett !