Command boring

Package boring exposes functions that are only available when building with Go+BoringCrypto. This package is available on all targets as long as the Go+BoringCrypto toolchain is used. Use the Enabled function to determine whether the BoringCrypto core is actually in use.

Any time the Go+BoringCrypto toolchain is used, the "boringcrypto" build tag is satisfied, so that applications can tag files that use this package.