Remove OpenSSL

Removes OpenSSL and migrates calls to our own vendored BoringSSL (#14, #13).

BoolClaim handles strings

BoolClaim wasn't properly handling "true" and "false" as strings.

Apple/Google identity tokens

Adds commonly used AppleIdentityToken and GoogleIdentityToken structs. This includes code necessary to validate the apple/google provided identity data against their respective JWKS elements.

This patch also restructures the project a bit to move classes into their own files with hierarchical folders to make it easier to find the items you're looking for.

JWKS.find

Adds new methods for finding JWKs from by identifier and type (#10).

let jwks: JWKS = ...
let signInWithApple = jwks.find(identifier: "AIDOPK1", type: .rsa)

Fix Payload Verification

JWT verification using JWTSigner and JWTSigners now correctly invokes JWTPayload's optional verify method. (#6)

JWTKit 4.0.0 Beta 2.1

• Replaced all fatalErrors with Swift errors.

JWTKit 4.0.0 Beta 2

• Separated from vapor/jwt into new repo
• Removed JWT type and split functionality into JWTSigner and JWTSigners
• New internal JWTParser and JWTSerializer types to reduce code dupe